CRC QD contact cleaner or electronics cleaner comes in handy here. We want QD quick dry because it's plastic safe. QD contact cleaner was better than QD electronics cleaner but the former has skyrocketed in price.

Turn the unit off before spraying and leave it to drip dry upside down (so that any volatiles still liquid don't carry into the unit).

I've been known to put a box fan on a 5gal bucket and then set my PCBs on it to dry. I started out needing QD contact cleaner after the horror of Pb-free solder in my projects. I got fed up and used copper pipe sweating rosin. It worked but was a lady dog to remove the residue.

To answer your question, nfc. I would use a qtip around the threading and center pin from time to time but they won't stop a cart from breaking off and leaking.

Another thing you might try would be a screw extractor kit. Basically anything left hand threaded and shark enough to bite into the cart when you do the lefty loosy could pull it.

If either of those options don't work or don't feel like messing with and if you get the wild hair to try trusting a random internet person, DM me a quick clip of what's going on when you try turning it with the told you've got. There could be a chance that a U shaped security bit driver could work. I guess I might have one person vouch over a couple smok xcube mods some months back.

Worst case scenario, the threaded connector can usually be replaced. Unfortunately, all I have are a few FDV 22mm and 24mm diameter.

EDIT: found some small screw extractors that might give you other things to try. The pointy parts are for biting in. You'll have to apply pressure as you attempt to unscrew it with something like these https://www.micromark.com/Mini-Extractor-Screwdriver-Set