I have a 2004 f150 extended cab fx4 with the 5.4. It has 172,000 miles on it and the trans was replaced at roughly 90k. I haven't really drove it in the last year cause I bought a 2011 f250. Anyways before I parked it I had a transmission leak. I thought it was from the pan cause that's where it was dripping from and it was covered. I took it to my mechanic and he replaced the gasket but said he didn't think that was the problem. He said he doesn't really deal with transmissions but he thinks it's coming from where the shifter linkage comes in. Well as he thought it was still leaking. Well I wasn't concerned at the time cause I was getting a new truck. Back around March I needed my truck and my wife wanted to use the old one cause we were supposed to get a bad snow storm. So I topped the truck off with fluid cause it was low from leaking. I took it for a drive (5 miles) and it drove fine for awhile then slipped. I'm assuming cause I didn't have enough fluid in it. I bought 3 qts and probably should have grabbed a couple more.

Anyways now I'm wanting to sell this truck but need to get this fixed. Is this a common thing? Could it be something as easy as a bad seal some where? I don't recall it leaking when it was running only if it was parked and turned off. Im hoping I don't need a new transmission.