I wonder if mineral spirits would work. I've been thinking the about doing the same to a frame that was very badly primed (it looks like directly on top of the old paint/decals).
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"