DavidL

Level isn't the issue.  Twisted chassis can be.  That's where one leg is too high / low.  Out of level is when two legs are not at the right height.
Twisted chassis is a bigger stress on the RV for flooring and slides.
But, take the popped tile out and inspect the subfloor like fasthobie16 is suggesting.  If that looks clean, mold free and dry, then possibly chassis twist or something heavy walloped the top of the tile.

I don't know.  If you had antifreeze in the fresh tank last year, and filled it, it should have gotten diluted.  The whole tank would have had some antifreeze smell, but not much color dependent on how diluted it was.  Certainly the better way is to Springize the system by putting fresh water in, and pushing all antifreeze out, shocking the fresh water with bleach and a full tank, run the bleached water through all fresh lines, let it sit for a few hours, and then completely flush the system again and refill and use.  Don't forget you don't run bleach or antifreeze water thru water filters (like charcoal type).
Maybe there was a line that you never used since then?  Like a second bathroom sink that  never gets used and there was still antifreeze in that line?
Either way, just sounds like the Springize was never completely done.  No problem other than some bad tasting water.

RV dash AC is just like auto, just longer lines, less sophisticated control systems and easier access to the parts.
Ports are either at the compressor (on the motor) or next to the evaporator or both.
 
If an auto shop wants to, they easily can diagnose / repair / recharge RV dash air.
 
rooftop units are considered generally not serviceable ie: replace them if leak.
Are you sure on R410a?  Never saw that on an RV.  R134 like auto.  And we are talking Dash air, not roof air - right?

This is the muffler I put on my ISM500 
https://www.amazon.com/Aero-Exhaust-Performance-Muffler-AT5050XL/dp/B07HZ3NVBX
 
I would also post an audio clip, but it sounds very much like Bliksem's...maybe a very small touch less muffled.
Where it sound neat (and the only time I hear it in the driver's seat) is going up Vail Pass thru the tunnel and floor it 🙂
 
It is straightforward plumbing job.  Just measure your sizes, get pipe / adapter / clamps to match, get some quality hangers, ensure you are connecting to something solid, put some rubber isolators in the strap and go for a drive.

No magic in that connector.  If you can find the right one, awesome.  If it takes more than 10 minutes, just clip it and put some solderless bullet connectors on them right size for the wire gauge.  Just take a picture to get the right wire to the right wire. I would put some antixodent on them, and tape them up to make them water tight and move onto the next mission.

https://www.homedepot.com/p/Gardner-Bender-12-10-AWG-Snap-Connector-5-Female-5-Male-Yellow-10-Pack-15-162P/205861878
 
Keep it simple.  Crimp, connect, wrap with some electrical tape.