I would look at one of the rust stabilizers that BJH suggested and then use the diy spray in bedliner from the parts store to keep it from rusting again. I made a plywood sink for a darkroom using the diy spray bedliner and it is still going 3 years later.
Until I swap a keg somehow create a gas leak that I don't notice and drain it. Honestly I have never used up a 20 from serving, carbing and, pushing various liquids about in the brewing/keging process. Seriously keep a spare CO2 cylinder. My current 20 is going on 9 months on my 7 tap setup and...
Yeah, the slot on the top of the disconnect side for a screwdriver. Here is a picture of one taken apart. To make a free flowing disconnect remove the two parts on the left.
Pin and ball lock are similar designs.
Sorry about the bad picture quality.
You said that you removed the poppet in the keg, Did you remove the corresponding parts in the disconnect? If not you fermented in a sealed container and created a massively over carbonated beer.
I don't have a picture right now (at work) but this is what I am talking about.
https://installationpartssupply.com/14-Male-SAE-45%C2%B0-Flare-Tail-PieceBeer-Stem--Stainless-Steel_p_6668.html
Proof that rednecks exist everywhere and that our rednecks in the US have much to learn. German rednecks no longer have a need for the saying "hold my beer."
I built my immersion chiller, it is 75' 3/8'' in 3 circuits and with 51 degree water and my pump circulating the wort it takes 7 minutes from boil to pitching temp. It's almost too fast but then again I rarely do whirlpool hops.