Diesel 911, You don't need to defend your opinion! I certainly don't feel that your process was flawed, and I wouldn't expect you to have done extensive controlled experimentation just to be able to post your opinion. You conveyed personal experience, as I did, and left it at that. Even though you indicate a bit of a bias, you do have some justification for that bias, and you haven't suggested that using a brand you don't prefer is a mistake. That's pretty well balanced.

The previous owner of my '79 240D managed to squeeze 18 years out of the original glow plugs before he needed to replace them. His second set was still in use when I took possession 10 years later. Were they superior quality? Maybe, but based on that information, it is still not reasonable to conclude that glow plugs should last for 10 or more years. Perhaps the facts that the car had had been driven less than 20K in its first fifteen years, and that the PO always used the block heater, year round, before he started the car every day, greatly extended their life. His experience does not give anyone reason to think that a set of glow plugs should last anywhere near that long. With a good data set, that single experience would be an outlier, and it would be (statistically) meaningless.

Point is, that there is no statistical evidence or results obtained from controlled experimentation to guide us in making this particular choice. I'll leave it at that.

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'79 240D