ORIGINAL: earlwb
One thing to do is to examine the glow plug element closely. You can use a jeweler's loupe or something else to get a good view of it. The glow plug element's condition can be very helpful in determining why you are ruining glow plugs.
Here is a good article on what to look for with a glow plug.
I had a scrapbook of "Duke's Mixture" articles that got lost in a cross-country move of my household. I'd sure like to find some or all of them. Do you have a source?
TIA,
CR