I was changing my oil the other day and when I crawled under the truck to unscrew the plug, I noticed that the rubber plug directly behind the oil plug (from hood to bed) was only halfway on. Whatever was in it had all leaked out. However, I had been driving it for several weeks without any problems. What on earth is that plug? It's circular and about half dollar size. The truck is a 1994 F-150 4.9 L, inline 6 with an automatic transmission. Let me know if y'all need more details. Thanks.

 

Is it on the bottom of the transmission bellhousing? Access cover for the torque converter's drain plug?

 

I'm not entirely sure what the bell housing is. I looked up some pics of the torque drain plug, but that isn't it. Oil is good, water is good, ATF is good. I have no clue what that thing is...

 

Sounds like the dust plug in the bottom of the bell housing to me . No worries , If nothing is pouring out .....

 

It would help a LOT if you could post up a picture for us.