It really sounds like you're resolved to get it, and I think you've already made up your mind.
In my humble opinion, the questions you are asking really suggests to me that the issues is beyond your abilities at this time. Most guys spend lots of time, through trial/error building up the courage and experience to properly rebelt boomboxes. While many members here make it sound easy, just keep in mind that it's not their first one. It's not hard once you have a bunch of them under your belt. But there are many easier ones I would suggest you tackle first. I really would not recommend any boombox this complicated for a "first" learning experience. Plus this one really seems far rougher than most so my educated guess is that there is more issues than just a simple rebelting. AND I really think that left door is not aligned due to physical damage, which might or might not be fixable.
Any technician worth his/her salt and has the training and experience to do a good job is worth $75-$100/hour. But then I live in a urban, high $$ cost of living location. Perhaps in other areas, you can get cheaper labor, $40/$50 hour. I would really think you'd be hard pressed to find a pro charge less than that. Then there is the obsolete factor. Most repair shops won't even touch an obsolete item due to lack of parts, schematic or other documentation. The reasoning is that they work on it, find it needs parts that are no longer available, and you decline to claim it due to it being an unrepairable item and you don't want to pay for the diagnostic time spent. So it ends up being wasted effort/time on the part of the tech. Also, no schematic means the tech spends 2 or 3 times longer than normal to trace. Sometimes without documentation, especially on tuners, it's not even possible to determine proper tuning specs and procedures.
I suggest you PASS on this one and spend a bit more for a nicer one, but it's up to you.
Just don't come back next week saying I got it -- it's not working -- how do I fix this, and please list the entire procedure.