Being a believer in lubrication, this may be taken with a grain of salt. I use what is typically available at the time needed! Spray lube like LPS-2, or Silicone-containing dry-spray seems good, but NEVER use WD-40.
Oil may draw dirt, but no oil draws poor frictional qualities between rubbing parts, too.
Certain solvents may be really bad news for the polymer used in this type gun, so stuff like brake cleaner, carburetor cleaner, and the like, might prove disastrous, keep in mind.