Only had mine on since Monday, and only covered about 100 miles, so far so good.  I really wanted a zorst that wasn't too loud, yeah, I know, it's an age thing  and this suits the bill down to a tee.  No droning, no vibration and no fuss.  Give it beans though and it sounds great, the closest thing i've heard to it is Ebizeds' Stillen on his 370, the best way I can describe it is rich and dark, hope that makes sense!!?