The sill on the drivers side towards the rear wheel I knew had a rust issue but when sanded back there were quite a few rust holes. I tried welding them up but there is too much rust. I bought a replacement sill some time a go knowing that I may need it. My question is, do I cut out the original sill right to the top where it is welded to the car or to the fold line that runs right along the sill ? Also should I take it back right to the rear wheel arch so I end up with only one weld part way along the sill ? I have ordered a joggler tool so I can overlap the join and weld through holes punched in the original part of the sill. The big job was the rust that was at the back of the rear wheel arch which went really well using a thicker piece of steel than the original. Using plenty of weld through primer hopefully will keep the rust at bay. Of course the area around the fuel filler had some problems and they have filled up well but I think it could be returning in the future. Is it a big job to replace the rear wing?

Just had a sill replaced, and it looks like they cut just below where it is welded to car, then angle ground (grindered?), to get closer. Then used some filler. .

 

More filler will make it totally smooth.

 

Don't forget to fill it with Waxoyl / Dinitrol once fitted.

 

Anybody know the sill grommet sizes to stop Waxoyl flowing out again?

clean up the rusted area and cut the bare minimum away to remove all the rot , always best to keep as much good original steel as possible 

Thanks for the advice. My mechanic friend said the best is to cut out the obvious rot and look inside to see what condition it is and extend the amount cut out if needed. He says that a cut should be made just below the fold line horizontally rather than right up to it is originally welded on. I have a complete Mk2 offside sill if needed. Of course I will flood it with rust kill and and waxoyl. I have filled a hole at the rear of the rear wheel arch which went well.