Q I am interested in acquiring a used BMW 728i. I have heard that the early models (1996) suffered from cylinder corrosion due to sulphur in the petrol. Is it possible to check for this, or would you expect the dealer to test before sale and can I therefore buy without asking? — SM from London

A You are right that some BMW 728s suffered from this problem and it can be an expensive fault to put right because it requires a new engine block with steel-lined bores, which can cost up to £3,000.

A car that is nearly nine years old is likely to be on sale with a non-franchised BMW dealer so do not assume the dealer either knows about or has checked for the problem. Early signs of trouble include an irregular engine speed when idling, difficulty starting (particularly when cold) and excessive oil consumption.

A call to any BMW dealer with the vehicle registration and chassis number will tell you if the engine block was replaced under warranty. If the answer is no then get the car checked by a BMW dealer before you part with cash.

The good news is that if the engine is okay then it will continue to be so as the high levels of sulphur that caused the problem have been removed from fuel, thus further damage should not occur.

Q I will be moving to France at the end of this month and am wondering whether to take my Lexus LX 430. Can I register a right-hand-drive car or would you suggest I sell or part exchange it for a left-hand drive? — JH from London

A There is nothing to stop you re-registering your right-hand-drive car in France, but you will have to go through a lengthy administrative process. To begin the registration or immatriculation process you’ll need to go to your local préfecture or sous-préfecture (chief, or sub-regional administration centre) to pick up a registration document.

You will also need an official document showing the vehicle conforms with French standards, which is obtained from the Direction Régionale de l’Industrie et de la Recherche.

These documents, along with proof of purchase, original registration document (V12) and proof of your residence in France must then be taken to the “carte grise” (literally “grey card”, meaning vehicle registration document) offices at the préfecture or sous-préfecture.

The process in theory takes 4 to 6 weeks and costs €200-€300 (£135-£200). In practice it may take several centuries. You can find out more by visiting www.frenchentree.com which gives advice on a range of topics about moving to France, including re-registering your car.

You might decide it is easier to buy a left-hand-drive French-registered car. In this case you would be better off selling your car in the UK and buying a car in France, as prices are lower and the selection much larger. It will also reduce your paperwork.

Q There are a number of professionally applied products on the market that claim to provide a “permanent” shine and a protective coating to car bodywork without the need to apply polish. Are they any good? — BW from Twickenham

A These products will provide a long-lasting shine if properly applied, although none of them claims to be permanent. They come with guarantees of three, five or seven years.

The products work by creating a seal over the car’s paintwork, protecting it from fading caused by ultraviolet radiation, road salts, pollution and acid rain. The surface is also more resistant than normal to bird droppings, tree sap, and hedge scratching.

The products with the longer guarantees require some maintenance, typically a monthly wash with a named shampoo and an annual inspection. However, it means no waxing or polishing is necessary; surface dust and dirt can be removed by light hosing from time to time.

Apart from the expense, there is no downside. A medium-sized car costs from £195 including upholstery and carpet protection, although it is important that the sealant is applied professionally — a process that usually takes 4-6 hours. Each product offers a different guarantee.

Clean Image Advanced Valet Centre of Chelmsford, Essex, has details of all leading sealants, complete with a review of their relative effectiveness. Go to www.clean-image.co.uk and click on “paint sealants” or telephone on 01245 350 035.

Q My mother has arthritis in her left knee and I am looking for a new vehicle for her. It must have automatic gears, power steering and plenty of space for the driver, with seat height neither too high (as in 4x4s) nor too low (as in some saloons).

I have up to £10,000 to spend. Any suggestions? — FC from London

A An MPV may be the ideal solution because they are easy to get in and out of and offer bags of room inside. The only way to ensure the correct driving position is to trawl around car dealers trying them out. There is no shortcut if you want to get it right.

The biggest-selling MPVs in the UK are the Citroën Picasso and Renault Mégane Scénic, both of which can be bought second-hand for well within your budget. We would also suggest you take a look at the Ford Fusion and the Peugeot 307, both of which have height adjustment on the driver’s seat and generous accommodation. The 307 in particular may look more like a family hatch than an MPV but it has a Tardis-like interior and a relatively high driving position that should suit your mother.

Q I own a 1997 BMW 328i Touring SE fitted with rain-sensing wipers that sometimes stop without warning.

When I switch the engine off and on and activate the wiper lever they restart — although this is of little help on the motorway. The fault happens about three or four times a year. Help! — MC from Redhill, Surrey

A BMW’s technical department suggests the problem could be a loose electrical terminal on the wiper relay. If so, it could be making contact some of the time but moving around with vibration and cutting out on other occasions, accounting for the intermittent nature of the problem. Get your dealer or electrical specialist to have a look at this area.

Q I bought a Nissan X-Trail diesel new in 2003. When coming to a halt with the clutch depressed and footbrake operated, the engine continues to rev at 1500rpm for several seconds before dropping back to 800rpm. The dealer says this is a characteristic of this engine. Is he right? — AH from Crawley

A This does sound as if it is a feature of the engine and it’s common to many modern cars. It’s probably part of the engine management’s anti-stall system, which holds the revs slightly higher as the vehicle stops to take account of any possible high electrical load that might be demanded of it, such as the fan blower full on, headlamps and heated rear window operating at the same time. If the engine revs dropped straight to a low idle position, it’s possible that the load could cause the engine to stall.

E-mail your questions for our experts on any aspect of motoring to carclinic@sunday-times.co.uk or write to Car Clinic, Driving, The Sunday Times, 1 Pennington Street, London E98 1ST. Please give a daytime telephone number. We cannot send personal replies or deal with every letter. Please do not send original documents or SAEs. Advice is offered without legal responsibility.