It wasn't because of stress, a friend of mine connected the radio in the wrong way or something back then and the radio was damaged.
That is the very DEFINITION of "stress" in electronic terms. It was connected with reverse-polarity power. If a proper-sized fuse was installed, the diode should have blown the fuse and protected the rest of the circuit. But apparently something went wrong. Somebody put in a fuse with a higher rating and/or the diode failed under load.
Are you implying that everything else works OK? It transmits OK, and receives OK, and changes channel, etc. etc.?
It seems unusual that only the signal-strength meter circuit would have been damaged.
If that TL489C chip is blown, you may have a hard time finding a replacement in single quantities.
You may have to replace it with an LM3914 or AN6884, etc.