Three tricks I've tried, but none works everytime. One, I use a water rinse paint remover. It isn't very strong so it works fast on rattlecan paint, but much slower on harder baked on enamels. You have to watch it to see the first layer start to crinkle, then wipe it off real quick with a wet rag. Two, use a lacquer thinner. This will also remove rattlecan paint and may or may not affect the original finish. The third is to use a polishing compound (lots of work). You should experiment with an obscure area so if there are any glitches, they won't be so obvious. Lastly, you may just want to concede that nothing will save the old paint. Just my two cents.
Fred Durrette
Summerville, SC