I have a 1855 that the hydraulic oil cooling pump keeps loosing it's prime. The original pump has had several rebuild kits in it and what I thought was a good spare, keeps losing it's prime as well when it sits over night. 

I rebuilt the spare as well before placing it on the shelf. I'm guessing either the bore the shaft runs in is wore, the actual housing is wore where the gears run, or both. 

What I'm wondering is this, is their a aftermarket version available? I can still get one thru Agco, but at 900 bucks a pop, it's at best insulting for a dinky little pump that moves a small volume of oil and barely builds any real pressure.