I have friends that roller paint boats and they swear by the use of penetrol to level the paint.
Way back in this thread someplace we talked about it, sounds like you are having good results with it.
I plan on a wet sand finally this winter and maybe a couple of extra coats, I installed my door mirrors lower then I like while driving so I'm going to plug those holes and move them a tad higher so will need a little repaint. I will use penetrol then.