I think I understand both sides of this situation:
I work at a lawn mower dealership. From their point of view, you, the customer wants your approximately 40 year old tractor to work and perform like new. Or as near to like new as possible. And they don't want it coming back on them because they cut corners to make the job cheaper. [like using chinese parts.] They also probably have much more experience diagnosing the problems of machines made in the last 20 years. For instance, the intricacies of diagnosing a battery/points type ignition may not be within their realm of expertise. (The other mechanic where I work, has several more years experience in the mower repair business than I do lets me do all the old Kohler battery ignition work that comes in this shop. because he knows I have those same engines at home and probably can diagnose them easier and quicker.)
About 8 or 10 years ago I actually overhauled a M16 for my neighbor across the street. In a Wheel Horse. Just the parts bill for the job was over $800. (He wanted all OEM Kohler parts, and it needed a camshaft, That is why we took it apart.) The job did not include boring the cylinder or turning the crank, but it did include a new rod and rings, a valve job and a gasket set.
From the other point of view, you own a 40 year old tractor that is still capable of doing good work-if only it would work at all.
My advice, is if you are really wanting to keep and use this tractor, invest in the manuals, the tools and the time into learning what it takes to keep your tractor running. And the bonus is the satisfaction you get in knowing you did it yourself.
These guys on here will be glad to help as much as they can.
p.s. Low compression in those engines is usually the valves. Either they are out of adjustment or the valves and seats need work.