88 G20 steering pump leak

I have a 1988 Chevy G20 3/4 ton van 5.7 L ...I have made the van into a camper...It is a GREAT VAN ! we have been all over the USA with it...The power steering pump started to leak ...The tank on the back of the pump leaks around the edge where there is a big "O"ring that seals the tank to the pump back ...So I got a whole rebuilt pump ! with the tank part installed on the back and replaced it ... This is quite a job on this van to replace that P. S. pump...After a short time now the replacement pump IS LEAKING TOO ! same place at the "o"ring around the tank on the back of the pump ! ...Does Anyone have a good fix for this ? Could I seal it up with RTV Ultra blue or something or is there a different improved pump that will fit my van Maybe a pump from a newer van would fit ?? ...I hesitate to go get another rebuilt pump as I am sure now that it will leak too ...It seems to me that this steering pump on the older Chevy vans is not a good design ... THANKS ! CAMPER BOB :disappoin