power steering pump leaking?

Is it a Federal pump? I think it took three different re-manufactured ones for me to get one that didn't leak from the housing seal. If it is a Federal, don't stack seals on the cap or it wont vent off excess pressure, causing a leak.
It is a Saginaw pump which I researched to be correct for a 340 motor with or without a/c. Didn't last very long. I wonder if the synthetic fluid I put in the newly remanufactured pump as well as a rebuild Firm Feel gearbox had anything to do with the leak?? I was told synthetic would run fine in the pump?? But who knows....I understand there is one company that actually makes the new pumps and the resovoir, but they are near 200.00. trying to find out if it is worth the money to buy one of those???