Q: I want to remove the battery on my 2006 Opel Corsa Lite so that I can make sure the earth cable attachment point on the firewall is free of corrosion. I'd also like to clean up battery acid salts that have built up over the years. Is it necessary to fit a memory saver device to the car's cigarette lighter socket before I disconnect the battery? - John

A: John, what happens to the on-board computer on modern cars when the battery is disconnected depends on the particular make and model.

Generally speaking, the computer will contain both volatile and non-volatile memory - some of which will be lost if the battery is taken out of circuit.

On the Corsa Lite which, thankfully, is not burdened with a humongous on-board computer, the worse that will happen if the volatile memory is lost is probably that the trip meter (but not the odometer) will revert to zero and you may need to re-enter the security code for the radio.

Of course, the latter will have been hidden away in a "safe" place which will take two days to find! To avoid such inconvenience you can use one of the inexpensive memory savers, which plugs into the car's cigarette lighter socket.

These devices use a nine volt battery to keep the volatile memory alive while the car's battery is disconnected.

Q: I DRIVE a Honda Ballade 150. What are the early warning signs of a gearbox oil leak, and is there a simple routine check to confirm that the gear oil is at the correct level? - Nepo

A: Nepo, a thorough inspection of the underside of the engine/gearbox area will reveal an oil leak. Gear oil (used in manual gearboxes) has a characteristic smell that distinguishes it from engine oil.

The only reliable way to check whether the oil is at the correct level is to remove the filler/level plug and feel whether the oil is up to the rim of the hole.

When the oil is leaking so slowly that it doesn't make an easily noticeable mess, the danger exists that the level gradually drops to the point where warning signs become evident, by which time some damage has sometimes already been done.

The signs would be "sticky" gearshifts, unusual noises and a smell of hot oil.

Not all gearboxes are equally robust, but the tougher ones can usually survive temporary low oil, provided it's detected quickly.