Not sure if this will help since I don't know the Mexico TR model.
This worked with two other Becker models: remove the knobs by pulling them off the shafts (some knobs are held on by a tiny screw that must be loosened.) Remove any tone or balance controls (by careful prying).
The Chrome surround comes off with a gentle pull. Now the dial front can come off revealing two vertical metal bands screwed to the radio and holding the radio to the dash frame.
When the screws are removed from the two vertical bands, the bands can be removed. The radio can now be pulled out part way to allow access to the speaker wires, the antenna wire, the power plug, and any auxiliary amplifier connections.
Once these are removed, the radio can be taken out all the way.
Richard M, NYC