Hi Dennis
I have a Generac 16 kw that runs on natural gas. It was installed in 2014. It runs 15 minutes every Wednesday afternoon and has run during power outages a dozen times, the longest was a few hours so total hours on it are about 80. Last year I changed the oil and sent a sample in for analysis. Came back fine, oil change was unnecessary. It is installed in a favorable location, sunny side of the house, no dirt roads or plant fluff nearby etc.
Lawn mower maintenance is much more involved. Your generator may need more but you should get to know this friendly machine better. Bank the $400 in case you have to buy a new one when you are older. Then you'll have a new one, rather than a collection of receipts.
I did have to order oil filters on line.