The Traxxion rear shock is rebuildable. I took one off a bike with 166K miles on it this week for a rebuild. I've never seen a single Traxxion rear shock leak or fail in any way. They had a problem with one small batch of seals about 8 years or so ago but this has long been fixed. The Progressive spring is another option, but it is a 1,200 lb/in spring, and the stock shock won't be able to control it very well. I also believe that is too stiff of a spring for this bike unless you're pulling a trailer 100% of the time.