Case 1840 pump leak

I have an '89 1840 with a Sundstran-Sauer M91-46 pump that is leaking. The pump works normally but it is leaking from the gasket that attaches to the rear of the pump engine side. It leaks without pressure and is no worse under pressure. I have rebuild other types of pumps and transmissions but not this one. My question is, anyone have experience with these and are there any common failure issues? Any special tools or info I might need to fix this or is this something I shouldn't do myself?