Martin,
welcome to the forum. (We need a photo please.)
I put the original trim back on my car when I did a rebuild. Can be a bit fiddly but I don't think it is designed to be impossible.
Without seeing what you have I can only work on some assumptions. Has your car been restored or is it original paint. Can make a difference.
Each sill should have 6 holes, you should have 12 clips and the two pieces of trim. The trim is stainless I think. Each clip has a centre post that should slide back and forth inside the main clip body. I have included a blurry photo that shows two clips, the black one in the locked position. the grey one in the open position.
The holes in the sill can be a source of water ingress. Before you start you may want to try and flood the inside of the sill with some sort of rust converter.
As a test, lock one of the clips and try and push it into the back of the trim. The reason I note this is that repo parts don't fit as well as they should. It should click into place with a little force. Be careful not to bend the trim. This will give you an indication on how well the parts fit together and how much force you need to apply.
Start with the clips in the open position. I put some sealant around the hole (to stop water getting in), pushed the clip in and then tapped the centre post in till it was flush. Onnce the post is pushed in it is really difficult to get the clip out because the post acts as a lock.
If your car has been recently painted, there is a chance that the clips are going to be difficult to push in because of paint build up. A gentle sand will enlarge the hole.
When you have done one side line the trim up and push it on by applying pressure opposite the clip. Note, the trim is shaped so it is possible to put it on upside down. The trim should sit really flat against the body of the car.
Simple really. Is this what you needed of have I gone right off on a tangent........
Regards
Joe R
