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I didn't say Jap decals were better quality - they generally aren't, in fact, because the carrier film is too thick and needs trimmimng off, and they have a problem with white areas.
I've no idea about decals that are falling off... Perhaps it would work. Find an old kit you don't feel satisfied with, and try! That's the great advantage of the system I described, with the multiple layers of varnish - the decals can not fall off, as they are caught between the layers. Try it on your next one!
Gunze acrylic. It's not the cheapest, but there you are. (Tamiya varnish tends to 'powder' as you spray it, and can leave the surface grainy.) Dilute it with roughly 50:50 industrial alcohol to Tamiya Acrylic diluant, and cut the varnish till it is fluid enough to spray. That'll leave it shiny, so then, go over it with whatever enamel (better solidity) varnish you can find. I normally use Humbrol Mattcote, although as Airfix/Humbrol has just fallen through, I'M not sure what will be available in the future.