Turns out the check valve spring failed. It rusted and broke in two. Got a new one from SunOpticsUSA and slapped it in. Also got a complete seal set. But the old seals looked OK so I reused the old seals.
Cleaned the guts with Brake Clean (AutoZone brand brake cleaner) and pumped the liquid out of it. Lots of black greese and what looked like bits of metal came out. left it open to dry then poured in some Royal Purple 10w-30w motor oil to relube it.
Put it together and cycled the pump a bit to spread the oil. The pumped it to 2,000psi several times and then bleed it off to dump the excess oil. Not much came out. Used my Marauder for this task and was careful to not to let the pump pressure get high enough to pass air to the rifle. Then I topped of the Marauder to 2700 psi.
Easy pumping - seemed easier than when the pump was new. It pumps very easy up to about 2200psi and getting the last 500psi is not too bad. For now this seems like a nice easy fix for my broken hand pump. Took about two hours including drying time.
SunOpticsUSA suggested using whatever automotive motor oil I had on hand. Royal Purple is what I had on hand.
What say you - are either of these chemicals bad for the pump?
But his was just severely gummed with a blown O-ring....he'd been using it for 3 years straight and it quit on him.....I brought it over to my house and tore it down, sprayed it all out with brake cleaner...let it dry, replace the O-rings with 90 durometer.....lubed it all with Moly....put it back together and it's up and running great....even smoother than factory....
These little pumps get a really bad rap....but, I've done two FX pumps and 4 Hill pumps for friends.....the problem with them is cooling time....guys don't pump slow enough, and don't allow them to cool down in between fills.....
I think they're the best value for the money....My Son's has over 1500 fills through it, to 32-3400 psi in various guns.....