300TD Injection Pump pulls air Help!

[jackcrac]

My 79 300TD has a bad Injection Pump seal somewhere and I was wondering whether there where any easier/common problems I had not yet thought of. Im sure someone reading this is already starting to type LIFT PUMP but...
After cranking and cranking to get fuel up to the injectors I can get it to fire. It runs like a dog for a while, wont idle well, then starts to smooth out. I can see a large amount of air running through the Injection pump to Main filter return connection at High RPM. It seems to "cloud" the fuel with air. My first thought was the inline filter or lift pump so I installed clear vinyl hose between Inline filter, lift pump, lift pump to main filter, and main filter to injection pump and ran it again. The thing is i don't see ANY air entering before the IP/after the LP, SO... is my IP shot?? Could the gasket between the Lift Pump and Injection Pump be letting air into the Injection pump? Could the Injection pump to Engine gasket be letting air into the IP? Is there anywhere else I could look? What i really dont understand is: if the air is not entering BEFORE the Lift Pump(suction side), wouldn't I have an obvious FUEL LEAK (on pressure side) rather than air coming in? All the pressure of the lift pump pushing the fuel out? OR am i mistaken and the Injection Pump also has suction?