You definitely do not have a port block mounted on the hyd/hst pump. I looked at the parts diagrams for later sn 743s online, and the ones that do not have the port block on top of the pump appear not to have this bronze filter. So we might be chasing something that doesn't exist on your machine. This rabbit hole started from a noise concern. My 743 groans when moving, equally both sides, with no decrement in power or ability. I mentioned it recently to a hydraulic expert and he said these hydrostatic motors in the 743s made more noise than later series bobcats. So with no adverse symptoms, I use mine and don't worry.