How often do you guys re-slime your UTV tires? I've got some slime in mine that is 2-3 yrs old and was thinking of re-sliming. Haven't had a huge problem with flats but we also run in mesquite and pear. Have a good set of all terrain tires. Wanted to try that ultraseal bulletproof. Do you just de-air and add new slime on top of the old, or do you need to take the tires off and clean out the old stuff? That sounds like a bigger project.