I'm trying to install a new o-ring seal for a TH400 dipstick tube after a rebuild and I can't get the tube to push all the way into the transmission bore hole. The tube will slide all the way into the transmission bore hole without the o-ring in the grove, but when the o-ring is on the tube it won't slide all the way in. The tube still needs to be push in about another 1/4" for the tube bracket hole to line up with the bellhousing hole. It seems as the o-ring seal isn't compressing enough in the tube grove once it enters the hole in order to push the tube all the way in.

This complete car rebuild has been one step forward and two steps back,