Yes, post processing the part with acetone (I dipped it once in acetone and let it dry) totally solved the problem.
Good idea!
Its easy to leak tight FFF prints. Vapor polish, a self leveling epoxy coat or even paint in some cases (depends on part geometry and strength and whether you are sealing liquid or air and at what pressure). To the point of the original OP... you could make a leak tight part with more geometries without post processing if full infill were allowed.