Now that my wife has retired, as I have, we can't justify two cars, so my "too big" 2001/51 Renault Laguna Privilege 1.8, with 80,000 on the clock, will have to go. I say this with some reluctance, because despite the usual problems with electric windows and sunroof, this has been a fine car in the four years I've owned it. However, I can't contemplate selling it with a known fault, which I've been unable to solve over the two years since it became apparent.

All four tyres suffer a slow but steady loss in pressure. The valves are linked to the computer, so I can see at a glance how they're doing, and the nice lady who lives behind the dashboard reminds me if they get too low. The problem is worse in the winter, so I assume this is something to do with expansion and contraction. When this happened on my previous car (Rover 600, also with alloys),I had the wheels sandblasted and that solved it. This time, however, the firm said the air loss was coming from the valve area, not from degraded wheels. I bought new valves and had them fitted, plus having the computer reset, at some considerable cost, and the tyres were later re-glued, but all to no avail. The Renault main dealer then tried, but said they could detect no air loss from anywhere, despite submerging the tyres in a bath, at high pressure.

If it were possible, I'd be happy to fit standard valves, not linked to the computer, but Renault say that on this model the valves cannot be separated from the programme, and the display would permanently show "fault". So, I can't seem to solve the problem, and I don't want to try to sell without being fair. Any ideas?