If your going to remove the tail shaft housing and replace the gasket

Why wouldn’t you pull the valve body , loosen the rear band adjustment , push the pin out using your fingers on both ends as to not push it out all the way , just enough to expose the o-ring , and replace the o-ring ?

It really isn’t that difficult to do - Even if the rear band strut came loose or fell out , you can pop it back in contrary to what you read on the internet

I have done a handful for myself and friends , I am no transmission expert