I snagged a box of builts from the mid-60's, and all were painted with AMT lacquer (not terribly well) 91% wasn't touching the aged finish AT ALL.
Got out the ELO and at first it looked like that wasn't playing nice, either. But after a few minutes, it softened and I worked it for a while, but since I was down to about 1/2 of a tin, I decided to see if that started the ball rolling and sure enough, the 91 finished the job.