Great information Dany boy, be sure to post a link to any website info you may have to follow up on that information.

As for the lean/rich argument, let me clarify a little what I meant by a rich setting killing my plugs more then lean. Glow plugs really only last when an engine is tuned efficiently, if it is tuned incorrectly, the excess fuel, or lack there of, can harm the glow plug. But I found that most of the time the too lean setting is the easiest to diagnose, therefore happens the least. Especially with airplanes when I see a lot of guys tuning by noise and/or smoke, a too lean setting is rare compared to a too rich setting(In my experience, I'm not saying its true or false, just what I seem to see more so then the other) Depending on the climate, a engine running too rich can still run fine, with just a lack of power. To a novice user, this lack of power may be excepted as simply the way that engine runs, in the mean time, causing excess wear and tear on the entire engine, including the glow plug.

Also I noticed you said your plug was a long, double check and make sure your engine will work properly with a long plug, if your piston is getting too close to the glow plug, this could damage the element as stated in a previous post.

Good luck and good flying!

P.S., when you do solve the problem, let us know what you did!