inhibitor switch

[gbw2]

The inhibitor switch on my 850 T5 auto is toying with me. It seems to be a particular problem only after short journeys - if I drive around for a bit and then stop, she'll start again with no problem - but if I pop down the road and stop, she won't start. I have to do the little trick with the gear stick to start it but this seems to be getting harder.

Anybody any idea why this only seems to be a problem on short trips?

Does anybody know how easy a new inhibitor switch is to fit - I can get one for about £50 (unless anybody knows a cheaper source) but the garages want >£200 to fit it?

Thanks for any advice.

Gary