Interesting comment as in, in 30 years, all of mine have gotten a steady diet of number 2 off road and never mixed squat. I do add Power Service winter blend however at the recommended dosage (and biocide of course). never had a start issue. Cold starts are more dependent on a good and fully charged starting battery than anything else.
They sit in an unheated barn when in use and are never plugged in (my cab unit has a never used block heater, factory installed). The seal is on the plug and been that way for 20 years.