anode wearing strange--thoughts??

They work on a "line of sight" type basis to protect any exposed steel. Could be the bottom of the threaded plug is needing the most protection. If it was mine and I'd already bought a new one I'd install the new one. If not, I'd put a little dope on the threads and put it back in.

Don't get too carried away wrapping or doping the threads. It has to have a good electrical bond to the tank in order to work.