Hey guys, I finally got in all new o-rings for my System 3 cartridge filter and figured it would be a straightfoward job of replacing them all...

Well, most were pretty easy to deal with. Even the drain plugs came out without much of a problem (a little stuff, but they came out just fine)...

Turns out almost every o-ring has been badly cracked and rotted. So I go to change out the bulkhead o-rings and wouldn't ya know it, the nuts cause the fittings themselves to turn.

The inlet just spins and the outlet will hit the built-in locating tabs and I don't dare try to crank on it anymore to get it loose (for fear of breaking those tabs off completely).

I know I can order new bulkhead nuts and just use a dremel and cut off the existing ones, but that is quite an expense. I have little confidence that the o-rings are in serviceable shape (especially considering the shape of the o-rings for the cartridges were just horrible and the only "good" o-rings where the ones used for the drains and those were encrusted in white residue and totally deformed from long-term pressure) and I really don't want to deal with any leaks once my pool is installed.

Any and all advice on how to lube the threads to get them to break free would be greatly appreciated. I don't think any sort of lube used for regular metal nuts/bolts would work (would it?) like either PB blaster or WD-40, but is there anything else that would work into the threads to loosen them?

I haven't tried the drift and hammer "shock" method to try to break them free yet. I figure if there is some sort fo penetrating lube that would work into the threads it would be better to try that before shocking them.