Terri - thank you! Your write-up is exactly the situation I'm experiencing - seawater is not pumping thru the engine.
Given the location of the generator, batteries and inverter it is very difficult to trace things out (I'll be pulling things out once I start working on the unit). Can you confirm my suspicions from the pictures below?
I believe the seawater is driven thru the pump that is in the lower left hand corner of the picture (it has a separate small dedicated belt - driven from the main crank). Is that the only seawater pump on the unit and likely the Oberdorfer? I've included a picture from the back side of the pump and it's quite corroded as if the shaft seal has failed and may be where the air is incoming.
And can you tell me where you were able to source the impellor? (I also want to replace all the belts)
I suspect your write-up saved me a lot of detective work. Thank you!