I own a 1980's zero clearance fireplace. During my last cleaning, the rep said to me that the backplate had a crack. It wasn't too wide but I opted to have it replaced - since I felt caulking it was just a band-aid approach and if I ever wanted to sell the house, it probably would be mentioned in the report as an issue anyway. However, once installed (only the back panel was cracked) I noticed there was a slight gap between the new back panel and the original side panel. I asked if this was ok (since the gap was wider than the crack was, imo- and he had said sparks could get behind the crack) - he said it was. Soon afterwards I was watching one of those TV shows with an 'inspector' and he pointed out to the new owner that there was a gap along the back corner seam and said it was not safe. He cemented it (I'd don't think it was a zero clearance fireplace, but a standard brick one). I have not used the fireplace yet, but after seeing that show I was wondering if it truly is safe? If not, will caulking be the sufficient or would I need to replace the side panels so they 'marry up' with the new back panel (I'm guessing that is the reason for the slight gap)? Or am I worrying for nothing - since sparks couldn't get behind it and start a fire in the first place?