Leaks from those holes means there are some seals that have failed, or weren't replaced when the pump was rebuilt. The linkage between the diaphragms must be lubricated by crankcase splash, but there shouldn't be enough oil in there to leak out. Either get another pump, or go back on the "rebuilder" who caused the problem and make him fix it right!
Also, if your crankcase vent system (road draft tube, etc.) is clogged, crankcase pressure will cause a leak there.
Jerry
