Same thing happened to mine. I removed the rust with a fine grade emory cloth and occasionally rub down the shaft with a fine coat of grease, and wipe down with a paper towel so there's really nothing left except a very thin film. For lubing the guts, I use a spray lube similar to WD-40, except it supposedly has more silicone. I spray a little on a paper towel (not so much that it's dripping), and rub it on the inside of the tube with a coat hanger or something similar, then use a dry paper towel to remove excess. Then I give it several good, hard pumps with the nozzle end pointed down to blow any other excess out (don't want it in my tubes!).
I've been doing that for several years, and the hp-x is still doing fine.