I hesitate to call this a "repair" video since it was an easy fix, but check it out if you'd like to see inside a Panasonic SJ-MJ500 since I do open it and clean/lube it after prying open and cleaning the battery compartment.
This was a "steal" for less than $20 USD (2780 yen) with the speaker dock and power supply! Unfortunately, I didn't get the proper remote for it, but I do have some that work with it.
The Panasonic SJ-MJ500 (late 2005) was their last "Dockin'style MD" player that included the previous 50/55/57/58/59 generations of players. Those also had speaker docks that slid in/out. This last model is distinctive with speakers that fold in/out.
If you run into players that have their old gumstick batteries stuck inside, there are various methods to open the door without damaging them. Luckily, this was a quick fix on a late-model Panasonic. It was untested, but worth a gamble, I'd say!