Any competent mechanic should be able to perform tests and
maintenance.
Changing all that stuff may be overkill; how much run-time does unit
get
per year?

Well, it "exercises" itself once a week for 20 minutes

BUT

In the last year there have been only two power outages: one for five
hours and another for two hours. However, this is much less than a
typical year.

Whose engine is it? Onan?

It's Kohler unit

I'd rotate fuel-supply, given the option.

500-gallon liquid propane tank installed 5/05 filled to 80% capacity,
now down to 70%.

Mary