1984 190E Transmission problem

[dieselnutnj]

I recently purchased my first gas Benz, a 190E. It was an Ebay special, and while body wise she's nice, starting it revealed what sounded like a whine in the transmission. It sounds almost like the Trans pump is bad, like an old Ford power steering pump when the veins go bad. It went into gear alright and I drove it about 40 miles then got on it to get up a hill,, and it popped out of gear. Once stopped it went back into gear and was fine till I hit fourth gear and it wouldnt go into gear. It slips in reverse as well. The trans looks like someone rebuilt same. Is it possible that in assembly someone missed something and the pump is not picking up just fluid but air as well? Is there a gasket/o ring that seals the pick up tube from the filter to the pump? I've never had an MB trans that far apart other then replacing the broken servos in the older trans. I have no fear of taking it apart, or working on it, but if someone has had a similar issue it may speed up the process. ANY help is appreciated. Thanks in advance

Rick