you can safely put up to 3g of oil in that hyd sump.. I have laoders using that much to keep it from sucking dry with SA lift cyls extended.
I like about 2g in general.
if it's loosing prime as stated.. remov ethe plug from the pump and put in a pip threaded brass petcock... it's a redneck bandaid.. but works. can loosen to bleed each day... till you get it fixed correctly.