When I bought my Ford 420 industrial backhoe I was having similar problems, It turned out to be the suckshun hose collapsing It was long so I replaced it with exhaust pipe that I had a muffler shop bend and a couple short pieces of the correct hose. also , for your fitting problem , can you drill and tap for a small fitting in the flat on that fitting? I don't know how big it is, so that might not be possible. Good luck .
Rich