my dana 35 ttb is fitted with an ARB locker, the copper air line is run DIRECTLY through the middle of the bearings main cap, it has held like this for years
installer drilled a small hole ALMOST right in the middle
Let me see if I have a picture..
This is an older Ford reverse rotation dana 35 ttb ARB locker. I bought it used, had it rebuilt and installed about 5-7 years ago...
I believe the newer ttb style has a re located air line, so this is not required?? but it sounds like your dana 44 is....
has held up for years, with a v8 and 35" tires at 10 psi

I did break my front ARB once, but it had nothing to do with the end caps, it was the cross shaft inside the locker sheared... $350 later rebuilt again LOL
That pic is from having it repaired the latest time, you can see the cross shaft was backing out and slamming into my gears
after repair: