99X is right.........sometimes the gritty nature of the old fluid is what's keeping the thing running. I've seen exactly what he said happen.......change the fluid and the thing starts screwing up big time. Also pressure flushing is a big no-no........
bmx.....yeah, it's fairly simple and straight forward. Buy a shallow bung kit and pick a spot in the pan that doesn't have anything above it, or in close proximity and either drill or punch a clean hole that "just allows" the bung to fit. I mig mine in, but they do make one that has an inside flange and outside threads with a thin thread on nut/collar. It comes with a thin brass O ring washer. Layer on some red locktite and snug it up....good to go. Never seen or heard of them leaking, but I prefer the weld in ones. Most guys don't bother and I can appreciate that, but knowing stock clutches like I do, I like to get some of the crap out in the interim. The quality filters are usually good for 100k or so, but having the ability to change the fluid in between stretches things a bit more.