I pose this question because Harley recommends 50,000 mile changes and there are a few who have reached that mark. My dad decided we would pull his fork legs and have a friend of ours rebuild them with Traxxion AK20 cartridges. The forks have 43,000 miles on them and when our friend pulled them apart he found the oil like sludge and the forks sticking instead of cycling smoothly. It used to be Harley had fork oil changes every 25,000 miles, I think Harley had it right at 25,000 and wrong with the 50,000 mile service interval.