I like the boiling to clean them up but I recommend putting them in White Wine Vinegar for 24-36 Hours. Then Boil again, leave dipped in Paint Thinner to deactivate the Vinegar for 20+ minutes, then a quick water bath. When I did this, there was a very light patina of rust on the parts within 60 seconds. Hit it with 0000 steel wool and wipe off the remnants. Paint as desired.
I've tried Coke in the past but you do need to keep a close eye. Lemon juice will work as well but will take much longer.
Good luck!