Dead 1989 Sony CDX-R77

Just acquired a Sony CDX-R77. I hit it with 12v of PC power supply juice and immediately smelled the dreaded smell we hate in electronics. It appears to be coming from inside where the wires go into the unit. I circled it in the attached photo. And yes I used a multimeter and had the +/- correct.

The unit was very dusty on the outside, but the inside looks pretty good for this age!

Any ideas what my next step is, or who repairs vintage units?

I'm pretty tech savvy.

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