Hello am looking at E36s - 316i-320i and noticed some things. One that looks okay has "bulutong" and rust on the edge of the upper doors. All four. What does that mean? It seems that the paint is orig and it is mostly stock. I see lots that are not stock and have modifications which I too am wary over. But is that bulutong a bad sign? Since it seems all mechanically there and only prob is that the fuel gauge doesn't work. Everything else seems tight and isn't it better to look at mechanicals first over cosmetics or would that bulutong be a major headache? Also its seals seem okay considering I see some older BMWs with really worn seals.

What are the common red flags in looking for a pre-owned beemer?