Saving very old decals

I tried to use a very old set of Micro-Scale decals this weekend (how old?–the instructions are in Latin) , but the numbers fell apart when I attempted to slide them off the backing. Anyone have any tried and true ideas to salvage these decals? I’ve heard of spraying them with some form of clear coat but have no experience with this. TIA, Ken

Try swabbing on Microscale Liquid Decal Film.

I saved some with a $1 can of clear coat. (couple of light coats)