Sta-bil, yes.
When I bought my house, I naturally needed to buy a lawnmower, and at the same time my Dad bought a new one. I used Sta-bil religiously, he didn't see a need for it. A year later, he had problems with the mower while mine kept running along, and did so without issue for another 11 years.
Maybe it was just coincidence, but he stopped having problems with his mower when he started using Sta-bil as well. If nothing else, it can't hurt.