My son bought a 2000 Ford Explorer with 88K miles on it from a guy who said the transmission was going bad and slipping. It was about a quart low, we added fluid and he has drove it for a couple of days and so far it seems to be okay. The fluid is pretty dirty and we were going to change the filter and add new fluid. Some have said not to change the fluid if you think the transmission is going bad, the dirt and grit in the fluid is keeping the transmission working.........new fluid may make it slip worse. I say put in a new filter and fluid and see what happens.........what's the opinion??