Transmission leak woes!

Thats another one of those little tips that isn't found in the average book(s) of how to.
When a dipstick tube is installed with a new O-ring it will pretty much position itself centered and leak free. Vasoline and careful assembly will be in the book(s).
When a dipstick has a teather/fastening strap, that strap is made of nearly nothing.
It could have been distorted during removal or whatever.
Your mission is to hold that dipstick tube in its self set sweet spot and alter the teather as needed to install a fastener. Otherwise the fastener will pull the tube out of position and create a leak.
Millions of transmissions have a plastic plug in the pan that once covered the dipstick opening in the case. That's because the factory had determined that the tube with its new and correct teather shape should be one of the last pieces installed.