The steel sunroof on the old Rover is pretty rotten and I've got a good secondhand replacement. The rest of the bodywork is pretty good considering it's 25 years old and has lived outside all its life. The sunroof is a known problem, not available new and fetch high prices secondhand.
It consists basically of a u section perimeter frame that the outer skin is welded to. There is a rubber seal clamped to the frame by steel strips on the other side of the seal, fixed to the frame by self tappers. On the old one these steel strips are rotten too, as is the frame. From the outside only a couple of paint blisters show.
Now clamping two bits of steel together with self tappers direct into steel is a recipe for corrosion if moisture is present - as there will be here. The seal is only partially effective and a tray underneath the roof carries any water that gets past it to drains - one in each corner of the car.
So I'm wondering about fitting plastic bushes to take the fixing screws. The frame they screw into has no rear access, so it has to be something like a self tapper. Snag is the self tappers are tiny. Perhaps only 3mm threads. And quite short - there isn't much depth to the frame. You can get this sort of bush for other things around the car - like say numberplate fixings where the plate is fixed direct to the bodywork. But all the ones I can find are for much larger screws. Any suggestions?