[KTL]

I have a few of those case fittings if you'd like a good used one.

I would try to put the fitting in place with a new sealing washer. Which makes me wonder, was there an aluminum sealing washer installed under the hex of the fitting? Maybe that's why they used teflon tape (that's a hack......... I hate that stupid tape) to install it.

When installed, the threads should be locked in place with high strength threadlocker. All the cases i've worked on have had the fitting threadlocked in place. So as long as you can get the fitting to grab some threads in the case, you should be able to get it to seal. The aluminum seal ring does the sealing, not the threads.