Ricardo,


What fuel are you using???

When you use fuel with 0-5% nitromethane and 20% oil half or more Castor, as I do... Well, I have never had to change a burnt glow plug.
I have two such engines, both still with the original glow plug (Novarossi C6).

Too short a tuned exhaust system will burn out glow plugs, so even though this system is set-and-forget (it seems this engine was produced over 3 years ago, still having the old style carburettor and the neutral head - see photo of new model), you may want to use a 1" (2.5 cm) longer silicone coupling.

Then you can see how your glow plugs hold up.

But the main suspects are too much nitro, or too lean a mixture.