Front-End Loader Davis 102H loosing fluid out the vent

[Carl in CT]

Hello, I have a MF 202 workbull with Davis 102H FEL and Pippen backhoe. The FEL is not lifting smoothly or strongly and I think it is low on fluid. When I added what little fluid I had around (a gallon maybe) it worked slightly better but not much. Funny thing is despite apparently being low it still spits fluid back out the vent. When I first got it that happened a lot and the previous owner said its normal because he had just filled it but it worked great otherwise, very strong. When I used it last weekend it gurgled and spit out fluid as usual and it clearly had air in it. This is not the original control box so I am not sure if I am supposed to fill it through the vent or not. That's what the previous owner said to do but it seems like their should be another filler somewhere. Trying to fill through the vent takes forever. Here's a lousy pic with the vent cap circled.

Any idea what's happening? I can't find a filter anywhere, could it be clogged somewhere or is it just out of fluid? How do I keep it from spewing out from the vent so much?