Removing stubborn screws from kit

[Naushad]

I've got a few car I am trying to strip down and rebuild.

Some of them are quite old.

Consequently, several of the screws have rusted..possibly all the way down their insertions and involving the threads.

I am finding it very difficult to remove these screws - particularly those that insert into metal parts e.g. posts.

For now, I'm leaving these parts covered in WD40/GT85 in the hope they will somehow loosen up.

Ain't too keen on Dremel or anything that might scar/damage the chassis aswell

Any advice would be appreciated!