Brian, have heard any rumor about the 3910X plug for the 206 not being manufactured anymoreMy view is that a spark plug is like a factory worker -- you replace them when they no longer do their job.
We replace them at every engine rebuild (some have been run a fulls season or more.)
Likewise, we have customers that replace them every race day.
I personally see no reason to replace a spark plug if it is sparking when it is told to.
Thanks and God bless,
Carlson Racing Engines
Carlson Motorsports on Facebook
33 years of service to the karting industry ~ 1Cor 9:24