Update...
Decided to replace the microswitch unit. Ordered and fitted the new unit from a porsche dealer (£25 inc delivery) - and this has fixed the problem!
It's also fixed the problem of me not being able to lock the car, and has now enabled the roof motors to engage! Still got problems with the roof, I think when taking it apart I've moved the mechanism out of alignment
but overall, I'm happier than before
