Onan 4KW Generator Oscillating Problem

My RV has an Onan 4 kilowatt generator I guess they refer to it as
 a Model:  4KYFA26100K   Spec K

On a recent trip, we started it up
and it started to "oscillate" or ramp up and down in power. It's sort of a slow up and down cycle that gets a little better under a load like the microwave oven.
We turned if off pretty quick and as soon as I got back home I started checking around to find a place to service it.
I usually call Camping World first. The guy I talked to said it was most likely the carburetor having the problem.
Camping World isn't an authorized service center for Onan as it turns out.
True of a lot of places that are authorized to sell Onan parts.
The guy told me that shops won't rebuild these carburetors and that it would most likely need to be replaced.
I checked around for an authorized dealer near me.
I started by calling Simi RV in Simi valley CA. Not too far from me.
As it turns out, they don't work on the Onan Generator either. They
referred me to Scandinavian Auto, also in Simi. Turns out this place is an authorized Onan dealer. I took it here and the owner Gert, works on the generators. He pretty much told me the same thing at Camping World about the carbs. He checked out my generator and ended up replacing the carb.
He also changed the oil, oil filter and fuel filter.
Pretty pricy deal at about $480.
He didn't have all parts the first time and I had to come back again to get the job finished.
My RV is a 2003 and I think my gen. is even older.
It only has 150 hours on it but it's over 10 years old as I write this.
I guess having not spent any money on the generator in 10 years, putting some money into it now, isn't so bad.
When I first got the RV, I ran the generator every month once a month for 2 hours. When I got back from my last trip, it sat without running for about 4 months. The carburetor gets pretty gummed up sitting that long.
I bought some fuel stabilizer to put in the tank and was told to run the generator a few times a month at shorter intervals like maybe 15-20 minutes a week. 
Not just 2 hours, once a month.
This stuff seems pretty good:  http://mystarbrite.com/startron/
We'll see if I can try to be a little better about maintaining it this time.