Mended, for £1
This is the problem - a burned contact in the F125:
This contact is slightly misaligned so was never making a proper connection with its counterpart and had burned a slight hole. I straightened it out and cleaned the surface up with 1000 grit paper, greased this and all the others with contact grease and reassembled it. Mike then helped me fit the repaired switch on Saturday and it now selects gears and drives round the yard just fine
Its not quite roadworthy yet though since it leaks oil enough to embarrass BP
Everything is dripping underneath including both manifolds and both cats and it visibly smokes while idling! Its mostly coming from the cam covers so it'll need a thorough clean and then new cam cover gaskets so I can see what else is leaking. It also needs front upper control arms and a CV boot so a little bit of work still to do.