I just bought a reefer truck with a MD-II-SR reefer unit. The system says it has a little over 9900 hours on the engine. every thing runs great I ran the system for a few hours and got the temp down to 10 F. More then cold enough for my fresh Farm Veggies. My question is this what is the expected running hours of the system? Should I start saving for a rebuild or replacement unit soon?