Our experience also, with the 12-14 and the older 8.5 units.Good sign.
The Kohler generator 20RESC is a good product. We have put in many of them, and their predecessors, with little difficulty. We load test those we install via a small load bank-to verify gas supply, which is by and large the most problematic portion of the generator install, and is often found to be wanting in flow and capacity.
As an aside, I had a customer who lived off the grid, and over the course of about 10 years put over 5,000 hours on his little air cooled Kohler 12RES, and in the years that we dealt with him, he had nothing other than minor maintenance items as you might expect: a starter, stepper motor, and the like, and of course regular maintenance items.
The 20 is not approved for off-grid use, in case anyone is reading and contemplating. It is a little confusing in the spec sheet.