SpudFiles

Thanks all, but I think i'm just gonna have to redo the piston housing. Not a huge deal, just means I have to buy another part (the extender thing).

I don't really know what your setup looks like, but can't you put a rubber bumper in there so it doesn't get hit (as hard)?
When I had an aluminum piston smash into a 3/8" steel nip it did cause leaks, and it also generally pulverzed the threads. I globbed on solder and jb weld to seal it and it smashed the crap out of them too.
After I put a chunk of rubber in there I didn't have anymore trouble.

Get rubber washers with an ID the same as the OD of the steel fitting you are worried about. (Garden hose washers ?)

Now stack and glue enough of them, to bring the bumper surface past the steel fitting.

Done.

If you have to grind any of the steel fitting away, on the inside, don't grind too much.