Renovating a GK 200MB

[Snipedog]

I picked up a cheap GK 200MB combo, mainly for recording / monitoring. Sounds basically good, but I think it has been modified, and that's produced some problems with the sound. I wondered if anyone had one and could guide me in bringing it back to working order.
The mains transformer is mounted halfway up one side of the speaker cabinet. This seems to be radiating mains hum into the amp, and it looks like it was originally at the bottom of the cabinet, below the speaker and further away from the amp, is that right?
There is also a hard rubber bung loose in the cabinet, should that have been wedged and glued between the back of the speaker and the back panel of the cabinet ?
I wondered about replacing the mains transformer with a toroidal to reduce radiated hum for quieter recordings. Any thoughts?

Thanks for any help from a Newbie.

[garagebassman]

My (90's-ish ?) MB150s combo has the rubber insulator at the back of cab wedged between speaker with a screw going through the rear center of box.
Don't know about the guts of 200, my electrics are all contained the "upper level", just speaker in the lower section of box.