Decal Transfer

I concur with Phil.  Old decals both disintegrate when in water for a long time, and the water soluble glue takes much longer to release.  Further, even if you do rescue the decals, the glue may not hold very well when everything is dry.

One can prevent the the disintegration by coating the decal with a clear solution sold for that purpose.  There are several brands available at the hobby shop.  A decal solvent may help the adhesion problem.

In this day of inkjet decal paper, I always scan decals of very old kits before I try to apply them.  If the decals do get ruined, I may be able to duplicate them.

Old (aged) or defective decals sometimes have a tendency to disintegrate when dipped. One very good solution to this problem is Microscale's Liquid Decal Film.  Paint it over the decal, allow to dry, cut and apply as normal. You should be able to find this at most well-stocked hobby shops. This stuff is a lifesaver..