Warning: check your soldering iron tip before you ruin a $300 board

I was recapping a Nikon F3 meter board last Tuesday and my iron tip had a fine layer of crud I never noticed. The solder just balled up and I dragged a blob across two traces, bridging them and lifting a pad near the edge connector. What saved me was a $4 brass wool scrubber I grabbed at a hobby store in Boise, not the wet sponge I had been using for 6 years. Two quick stabs in the brass brought the tip back to shiny and the next joint flowed like it should. I finished the board, metered it out, and the meter reads dead on now. So has anyone else had a tip go bad slowly enough that you blamed your own hands instead of the tool?