Something I like to do sometimes is challenge myself. Maybe this shouldn’t be one of those times 
I know there are several places out there doing 8-track repair. Wondering if anyone has undertook this adventure on their own, what it may take, and where they found parts to do it? I am happy with the Resto Auto sound in my 67, and it’s nice to have the FM to listen to, but I think it may be more fun to pop in some of my NOS country 8-tracks I acquired, especially my old Slim Whitman one still in the box. (I know I’m a nerd 
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Never tried an 8 track, but I do like new challenges. A couple questions I always ask myself ahead of time. Does a mistake result in catastrophic consequences? Like the EPA condemning my property. Will this require ridiculous amounts of money be invested? If the answer is no to both of them I’ll usually try it myself.
Rebuilding an 8 track radio is going to be the same as rebuilding any 1960’s era electronics. You will need to replace all the old style capacitors with new ones of the same or very similar value. Then replace the transistors. Finally clean the head, and install a new belt. After that you could figure out if any of the switches need replacement, or if a simple cleaning will do. Last thing would be cleaning the push button assemblies so that they might have some chance of functioning.
I had my 8 track rebuilt by a “professional” who claimed to have done all of the above. It plays, changes tracks, and has an AM radio that works. Sound quality is iffy.
Great care is needed in de-soldering parts on 50+ year old phenolic (type of bakelite material) circuit boards. The connective copper pads will easily come off if too much heat is used or pressure. After many years of fixing these other issues are hardened plastic? pushbuttons that break off when pulling them out to set a station and tuning shafts that are corroded and won’t move. Always pullout the flywheel and polish it too reduce the friction. Most purchased 8 tracks always suffered from low fidelity 500Hz-8KHz because of the high speed copying process during manufacturing and on the playback side due to lousy tape heads that were designed for a higher output voltage ( for simpler/smaller amplifiers) then frequency response. 8 tracks recorded on a home recorder usually sound better due to the slower speed (bias waveform) and a better direct source signal. My suggestion would be to buy several similar units (part number) and make one that works