So I am not 100% convinced I can name the problem, but all my experiments lead me to conclude that my input connection is lose in the head of my amp.

I have a Marshall 100MG and while it's not my favorite amp in the world, it's all I got at the moment. Is there a simple way to dissemble and fix it, or should I take it to the shop?

I am not a very good mechanical steward, so my confidence is low.


EDIT: My band has 5 shows this month, including one this Friday, so I'm inclined to hurry. lol
I'm reluctant to help anyone fix an MG, but assuming it's an input jack issue, it's most likely one of two problems.

1 ~ A solder joint has broken
2 ~ The jack is worn out

Either way will require precise soldering work on the amp's PCB. If you've never done PCB soldering, I recommend you start with something simpler and take the amp to the shop. If you've never done soldering at all, I suggest you learn how but still take the amp to the shop.
ESP LTD EC-256 and a Fender Deluxe VM