Hi. Just wanted to get a few tips from the experts about a used VC Defiant Encore Model #0028, Serial Number 18820 (approximately 22 years old). Sellers says unit is in good shape but needs new catalytic combuster. Unit is black and paint is original and in good condition. I have heard some stories about warped backs? What should I look for to make sure it is a "good" used stove. I will be out $400 plus drive time and cost of new cat. Thanks for your help!