I love seeing this beep and dig forum still so active. I've checked some of the others and they are dead lol.
My 2¢ on Tesoro....
They're pretty much rough and tough machines. They're solid state built and last forever. Many of mine are pushing 30-49 years without ever needing repair.
Som sommon issues you may run into is the O-rings on GB pot may need to be replaced as it wears out. The friction of it is all that's between the stem and the actual pot stem. That's why you can keep turning them the pot stops but the cap riding the oring slips
Also maybe some deoxit for the pots.
Other than that the parts they used are meant to be used millions of times. Like their pots the expected service life was like 2 million end to end turns. Lol they used quality parts and that's why they last.
Obviously try not to drop them. If you do and something wonky after most times you can open faceplate and see a solder joint snapped and just resolder.
When I modded my cobola with GB I was happily surprised with the components inside.
Now their surface mount pots meant to be set in factory or a couple times later I'd be more careful (like the internal ones for GB and sensitivity and threshold inside compadre) their service life is only like 100 times lol. And you need an oscilloscope to fix if you tweak them too far out of whack.
Anyway if you buy a tesoro used, check it right away with some air tests and swing around your yard and look for falsing.
If it runs good when you get it it'll keep running good unless you break it.
If it is falsing or acting weird, eBay has money back guarantee even if seller doesn't accept returns. If listing says works good and it doesn't you'll get your money back.
Breath easy. These tesoros will outlast many of us even with normal use.