I replaced mine mid last season after about 20 cord. In retrospect, I could have gotten away without it but I wasn't willing to pull the cat mid season without having the new one on hand as the King is our sole source of heat. The original is now cleaned up stored away in the box the new one came in for use in 5 or so years. I think the new one was ~$250 delivered from firecat. Small price to pay for what the King does.
Im going to order a backup and do what you did every other year, how did you clean the original? Did you do the BK suggestion with the vinegar?