Well, you've got a Hydro Gear.
I'm not really up on these units. They are pretty different in design, and set up from the Sundstrand pumps.
Take a look here:
HG linkage.jpg
In the pic, circled in red, is a set screw. It holds the arm on the shaft. Make sure it's tight. If it is, then the problem may be internal. I personally wouldn't tear one of these units apart. You can buy a good used ported Sundstrand unit for around $125, or less. I'd get a different unit. Mainly because, if it is internal, and it's what I suspect, it will cost more to fix than to replace. Good luck!
