Bobcat B250 drive problem

First off I have to say this site has helped me out a lot since I found it a while back. Sure seems like there's a lot of knowledge floating around on here. This is my first time using one of these forums so hopefully someone on here can help me out. I'm working on a Bobcat B250 with no drive. I'm the 2nd mechanic to dig into this machine to try and fix this thing so here's the story I was given. The problem first started as a loss of power in the drive system slowly getting worse until finally the machine could barely move itself. Someone else diagnosed it as a faulty drive motor, which was replaced, still same issue. The machine sat for at least 6 months I believe he said before I got to look at it. Here's what I have found. I started with the charge pressure. Upon start up I have a charge pressure of 320 psi @ 1000 rpm. With the wheels on the ground, as soon as I try to drive either direction the pressure drops to 0 and stays there even if the travel pedal is returned to neutral. The only way I am able to get the charge pressure back is to turn the machine off, wait a couple seconds and restart the engine. The pressure then comes back right away. With all 4 wheels off the ground I can slowly apply forward travel and maintain it at about 1/2 travel speed. Reverse I can only maintain about 1/4, any more than that and the charge pressure drops to 0. I removed the charge pump and the large valve body behind it to clean and check the valves. I found one needle missing from the the shaft bearing and some paste like filings in the replenishing valves. I replaced the bearing and cleaned all the valves, reinstalled & set the charge pressure & flushing valve back to spec, same result. I've tried turning up the charge pressure as well as the flushing valve with the same end result. My thought is that it must be dumping charge pressure in the pump once the swash plate starts to move, but I can't figure out why the charge pressure doesn't come back up once the drive pedal is back in neutral. Any thoughts on where to go from here ? Thanks, Steve