I have had limited experience with this problem, but I have had good luck with Testors Detail Bonder. I think the biggest issue will be with the overall condition of the decals. Last year I did a Datsun 510 kit from the '70's and the decals were very yellowed. While soaking the decals in water a substance like mud came off with a light wipe off in the water. The decals still laid down OK.