John Cribbin

As it's Japanese, there's a good chance they've used JIS screws.

I'd try Kent Armstrong, they have been doing custom stuff forever.

I'd guess box spanner, they have pretty thin walls.

For years, I've protected new cables and cabs with Armor All Protactant, you can get it from most car accessory stores. For old stuff. I wipe down with warm soapy water and use naptha for any sticky crud. Then I apply the Armor All. About once a year, I'll spray some on a kitchen roll and pull the cables through a few times, removes the old dirt and reapplies the protection.

You need agedhorse who is one of the guru's at Mesa Boogie and is very active helping with MB issues. I don't know if he is still active here, but I'm probably breaking a forum rule by suggesting if he doesn't pick up here, post the issue on Talkbass were he's certainly active. Good luck with getting your issue resolved.

Good luck for the op and a speedy recovery. OK here's the tough love. Don't ask a bunch of randoms for medical advice, it won't end well. You follow doctor / therapists advice. If recovery is slow, so be it. If you rush back before your body has recovered, you may cause more damage than you had pre op. Take care and be patient it will be worth it in the long run.

Years ago, I had similar with an Ibanez. I bought a cheap set from eBay to canabilise for spares. Something like this: https://www.ebay.co.uk/itm/134092048521?hash=item1f38824889:g:KjYAAOSwa-diX-Mo&amdata=enc%3AAQAHAAAA4BCk6H0dxo6Ge0VRB4He2isMz2NKWGvuUsoqocGBuJqIDBZ8M7RCj0XWkaykrhv7VnqxKnl3O%2B1gjqJYcblidgrn3p1UXBtgEYq457mznELCkblOfgzHX5LJP6rZQxrryEjRT9wSua%2Bpy73GrKIZrjVe7uDo5VVG7ntJmZdWPS2z49q4dxJu3buNallP%2FfyoCFyAdWxbLr%2FUx%2FKh3pXmqYbkPI%2BZKUYox4i%2BoqdW4bSoEXMiJx1CdSO16bbbJSAVSZePcINTQhqW9eiYcCkz%2BO%2FuEU6GfjGOXJ%2BLadYcyvhN|tkp%3ABk9SR6yJpenhYQ

You could used another sticker on the front, job done!

Depending on age, Peavey may be able to help. Other than that, you may be forced to keep looking at eBay until somebody offers a used part. If the demand becomes high enough, at some point, somebody will create a 3D printed part. In the meantime, I'd suggest velcro to keep the battery in place.

Fourth one down? https://www.sandberg-guitars.de/support/wiring-diagrams/

It's a bit difficult to work out without the above details but .... Working on the assumption that the loose wire has not strayed far from it's home, the bottom right connector just below the loose wire in the first two photos, does not have anything connected to it.

Bunion's diagnosis is the most likely diagnosis. Don't know your unit, so this is guesswork .... If the pots are soldered directly to the PCB, there's a good chance if you remove the knobs and loosen the nuts underneath the contents will come out. Or not as the case may be.

Now that's easy peasey lemon squeezy. Last one of those I dealt with I brushed on some Ronseal water based gloss varnish with an artists brush. Built up the level in several layers lightly sanding out any exess with 1500-4000 wet and dry. Finally using the T-Cut to bring up the shine. I used the Ronseal, because it's what I had handy. A tube of touch up clear coat from a car repair shop would do as well. There are those who use nail varnish or superglue on a scrape like that, but those are not methods I've tried yet ....

I've had good results using T-Cut on guitars, but I've not tried on a metallic finish .... My guess would be that clear coat is sprayed on top of the metallic in the same way they do on cars. In that case you should be fine. Without a clear coat, you would be polishing the metallic coat and that may be potentially problematic ...

Pure Tone Hmmmm ..... I've not used or have any intention of using them. I have seen on some forums a few people raving about them and how they will last longer than the existing jacks. Now considering we are all aware of thousands of instruments and amps from the 50's and 60's that still have their original jacks still working, come back in 2080 and tell me they are still going strong. They may sound good on paper. but in a guitar situation, I'd say they are nothing more than a solution looking for a problem.