OM 603 Priming issues

Hi All,

My 1990 300GD suddenly decided to make starting after sitting even an hour a bit of a problem. It seems to loose the prime in the fuel system. I can reprime by lots of cranking. The fuel filter is about half full when I open it up and the low pressure side of the system seems fine. I have swapped out the fuel pump and the fuel thermostat with good used components to no good effect. I have replaced the o-rings onthe fuel filter bolt and removed and retightened all the hose clamps at the fuel pump etc. I see no leaks in the high pressure system (externally). I am wondering if there are some seals internal to the injection pump that I am missing or maybe an injector is stuck open? The tank appears to be venting fine and not causing a vacuum.

Any thoughts???

Thanks,

Adam