You're probably aware of this already but luckily a lot of service manuals can be found online in PDF form.
Somewhat related but I was going through an older relatives belongings not too long ago to help cleanup and found a bunch of old manuals for various household things. The detail included in them was beautiful to see - full wiring diagrams, mechanical diagrams, etc.
Not official ones for John Deere tractors unless they were leaked from authorized service agents!
One example: https://assets.sia.toyota.com/publications/en/omms-s/T-MMS-1...