My TH350 is dripping. Been fighting this for a while. The dipstick tube was leaking, was the type with the "O" ring. Changed the "O" ring 4 times and gave up. Swapped it yesterday for one with the top hat seal. The dipstick is now not leaking but the TV cable connection is. Pulled it today and replaced the "O" ring. It's plastic with a squared off groove where the ring sits. Is the correct seal an "O" ring or is it something else? The reason I ask is the edge of the hole in the transmission that the plastic goes into is not beveled at all. Looks to me like it would shave the "O" ring as it went in.

Al 73 Nova, 454, TH350 with long tube headers, an absolute pain in the *** to work on this side of the transmission. Took me hours to swap the dipstick tube

 

There were two seal types on TH350 cables , one was an o-ring . The other took a top hat/boot type seal . Youre cable would have an o-ring groove in it i it needed an o-ring . If it didn't have a groove in it it took the other seal .