Stuck bulkhead on a Sta-Rite System 3 Cartridge filter

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.

I decided to soak the threads with a high pressure water spray, waited about 15 minutes, then used a drift and hammer to tap the nuts around... It worked beautifully...

So, my System 3 cartridge filter is totally rebuilt at this point. I put on a new pressure gauge, all new o-rings throughout, tested the air bleeder and it works as it should and with the new connecting unions I am all set to put it into service... I also added a complete waste valve to it and have it connected via hose to drainage so servicing it should result in minimal mess at the equipment pad. I am also placing the filter so I can get at the cartridges without having to step over piping and other equipment...

Long story short is that it is a filter that was used for 1 year and then not used for 10 before the previous owner pulled his in-ground pool. I got a great deal on it for $100 and the cartridges are just fine, just caked with a light layer of brown dirt gunk. I honestly don't think they used it for more than a couple months before they closed their pool. It was also kept inside because there isn't a bit of sun-damage to any of the labels and there is no corrosion or sun-damage on anything. The original cord ring is in perfect shape as well, even though I have found a place that has them for like $12, so they aren't very expensive to replace in the future. I will probably order one just to have on hand here shortly.

I had to soak the cartridges and then use an acid-bath to get the majority of the caked-in debris off of them. They aren't 100% clean, but they are good enough for the next couple months, since once I get my pool up and running it won't be too long before I have to close it for winter and I will then do another acid bath on them to get them totally clean (I used a really weak acid bath before, with 1/3 gal of muriatic acid to about 20 gallons of water so this next time I will use a whole gallon of acid for 20 gallons). So I have about $160 in the filter including the drain piping and valve, so I am pretty happy with such a good deal.

Thanks for coming back and sharing what worked. It may help someone else someday. :)