Have an 88 F150 with a C6 transmission. If I drive my truck at least every two days, everything is fine. However, if I don't drive the truck within 2 days, then it starts leaking tranny fluid. I replaced the tranny filter and the gasket. Everything looks okay, but the leak seams to be coming from the pan. I had a ford master mechanic look at it and he doesn't believe it is the tranny pan (believes it is coming from above and dripping onto the pan and down), but isn't sure what it is without removing the transmission or the exhaust (either is not easy to do). Before I rip into it, does anyone have any idea what the issue could be and any suggestions?

 

Look where the trans shift leaver goes into the trans, there is an o ring that seals the shaft, mine always leaked until I replaced the o-ring, if it is this, unless there is an o-ring seal at the end of the shaft, you will have to drop the pan, you also have to remove the valve body, remove the spring detent, remove the nut holding the linkage on, take out the shaft, and the o-ring should be in the hole where the shaft came out of. Reverse for assembly. Also you must pay attention to the valve body when putting back together.