Old
decals can be a real problem to handle,it sounds as if there were microscopic cracks or distessed
decals,once the solvent is applied it creeps underneath and is quite searching.One trick I have tried with old and valuable
decals is to coat them with something,clear varnish is perhaps better applied two thin coats,this has the effect of closing up the old age cracks and sealing the decal,best to experiment with a piece of decal in some obscure place on the model itself.