I found a local "generator whisperer guru" who changed the oil, and tuned it up. It didn't run well before and has run well in the two years since. It is important to run it every few weeks or so under load.
Periodically running the genset under load is good advice. However, "every few weeks" is a bit of an exaggeration. This is especially true with the propane version of the genset, for which this is much less important than with gasoline units. In my experience (14 years and two rigs) a few times/season is adequate to keep the commutator surfaces clean. If I had gas, I would do it more often, to avoid carburetor issues. Generally speaking, the propane units are less trouble-prone than gas.
I change the oil once a year and run it about every three months or so. It's the propane version. I did have to drop it from under the van, which was a major pain in the butt, when it quit running. Mud daubers had plugged the breather tube, so now there is a screen over it. I also adjusted the valves while it was out.