Burned Glow Plug in less than a month

[sgoodhart]

I have a 1981 240D that had two burned and bad Glow Plugs about a month ago. I replaced those and the car started fine. While I was at it I had the injectors tested and found two with bad tips although they were not the ones with the bad glow plugs. I replaced all the tips and had the injectors calibrated. The car ran fine for the last month, about 350 miles, and this morning it would not start. I checked the glow plugs tonight and found one that was no good. I pulled it and the tip was burned off. It was one of the same ones that I just replaced a month ago.

My question is what would cause the glow plug to burn in this amount of time ? Anything I can check ? I have obviously not cured the problem yet.

Scott