If you'd like to have them repaired, I think it's resonable since you have two basically same players. The Onkyo looks like the xp300, should be OEMed by Panasonic. Combining one working player should be no problem. I understand your feeling about your former lover. My former lover is an Aiwa XP77, with fabulous bass although a bit weaker than AIWA XP7. I'll keep its spirit young in my lifetime.
Warm will only affect capacitors on the mainboard. Having been used nearly 20 years since manufactured, the caps should be replaced totally. And all the reading parameters should be calibrated again, including Tracking Bias, Focus Bias, Tracking Gain, Focus Gain, Vco pll, laser power, and voltage of all power regulators. Furthermore, all gears, motors, feed screw, and all variable resistors should be lubricated. After that, you can use it for another decade.