these guys run insane duty cycles on their sanden pumps at 3000 rpm so they have done whatever they can to make these pumps last yet keep oil and water from filling their tanks.
you completely disassemble the pump, clean all of the old oil out, there are a couple holes you have to seal to isolate the two halves, vent the crank case pack everything with grease: cylinder walls etc. (a nice high temp high performance grease), re assemble making sure everything goes back the way it came out, voila!
the tread starter accidentally put a check valve in backwards and blew a chunk out of his compressor sending if flying into the radiator or something like that.
but he's been using his for 3 years and its still running strong.