Daox,
I had a similar problem with a heat pump project.
Standard pipe thread is tapered and relies on a progressive interference fit to work.
There are other pipe thread systems that do not rely on tapered, progressive interference to work. Instead, they use a flat compression washer. The straight threads supply force to compress the washer.
If you were crossing systems, it would feel gritty, because very small bits of thread faces were being sheared off by your struggle to make it seal.
One give-away is that the thread shoulder (male and female) has a precision-machined surface.
There's a good chance that the damage to the threads is not completely fatal yet. If the machined surface of the shoulder is still intact and undamaged, you may be able be successful.
Of course, you need the proper straight-thread part and the proper compression washer.
If the damage has been too severe, there's epoxy.
Best,
-AC_Hacker