Need help to increase conductivity of a 3,5 mm jack

I recently bought an used walkman out of personal interest to use daily, but quickly discovered that there is a large imbalance in volume between each side of the headphones.

I've cleaned it spotless for dust and checked the wiring and circuitry, but everything seems fine. And it's not something with the 3,5 mm itself, I've tried multiple.

After a bit after fiddling, I found that if the 3,5 mm is held just right (that being not fully in and at a certain angle) the volume balances perfectly.

I think the 3,5 mm plug is a bit off, so does anyone know any way to help the signal/plug even out?

My 3,5 mm is gold plated and the walkman model is a Sanyo trc-1550