Shaun-

Given what you've already done to the car, it sounds like you must have a problem with the hydraulics within the OD. You mentioned not being able to access the relief valve. I don't know exactly how it works, but I know that the valve itself is not much more than a ball and seat. If fluid is getting past the ball, pressure would be relieved from the pistons and the OD will slip. When I was investigating problems that I had with my own OD, I remember reading a post by a man who periodically machines that seat so that the ball will seal properly. You could very well have a problem related to this.

If I were you, I'd spend the $65 on the "mini rebuld kit" that IPD sells. Then I would spend a day or two taking the OD off the car and putting in all new rings and seals. It's not an extremely expensive procedure, and you've already taken this thing off and apart once so you'll probably have no problem the second time. (I had to do it a couple of times on my own car before my symptoms were completely eradicated.) If new internal seals don't work, you can still access that ball and seat with the OD on the car via the access plate on the bottom. But I would definitely look at it with the OD off the car to look for any obvious damage. If there is damage, it would probably be safer to take it to a machine shop for a professional resurfacing. I really don't know how I would do that myself without getting metal chips all over the place.

That's my take on it. Good luck with it, and let us know how things go.

Tim