Any Zero-Turn Mower Experts?

A little more diagnosing. I made a linkage adjustment to the left pump since I noticed it wasn't equal to the right at full forward position. It made a difference, until it had ran for a bit. Shut it down and checked the hydro reservoir and noticed a good deal of aeration in the oil. Seems to me like it's sucking some air from somewhere, but it doesn't leak. Possibly the crimps on the hydro lines?