You are correct. I diagnosed the same thing after disassembling. I found a thin glass filter with polarizing film on it which had burned from the fan sticking. The fan may have stuck from dust, lack of lube, or running the unit too long. After searching for ages for the lens which would seem like an easy and cheap replacement (the unit does not work properly without it) I found a couple from China but the cost plus a fan was about the same as a new unit some of which have upgraded fans.
If you get another unit from db look into putting a better fan in maybe? It’s not that bad to disassemble and the videos online are good guides
Hope this helps