Correct, an oil pump can and will fail with enough time. When they fail they fail to wide open for a safety measure.
When I reinstalled a new one on a 700, I made a driver with a piece of 1/2" dowel about 1.5" long. I notched the end to fit over the pump drive, then put a small zip-tie around it to keep it centered on the drive. Installed the other end into my 1/2" cordless drill. I cut 4 6" pieces of clear tubing and plugged onto the pump outputs. Zip-tied these together and primed the pump with the drill, pumping the oil into a container. Once I knew the pump was pumping out of each port, I reinstalled the oil lines from the motor to the pump, and primed those with the drill. Once this was done, I pulled the drill and the adapter off and bolted the pump back to the motor.
That pump went out at about 3000 miles. My current 700 has 3100 and I will be taking the pump apart this weekend to clean it. For whatever reason, the pump has the ability to lubricate itself using the injector oil, but has no way to purge the small metal filings that accumulate in it as the pump wears. Once these filings build up to a lethal level, they start to grind the gear parts rapidly. I figure by opening up the pump and flushing this excess metal out, the pump should last considerably longer (hopefully as long as the motor).
