Give us a better description of the glow plug (how the element looks) I'm currently using Mccoy MC8 or 9 and they last for a very long time I can't even remember when was the last time I changed it.
Sometimes I keep my 4tec running with out stopping the engine for over 45mins. always checking the temp not to get over 240 F after running full throttle for a few runs. If I remember well I broke the engine with Byron's 20% after a gallon changed to 30% and now I'm running 33% and never added any shims under the cooling head.
It is important to give your car a good maintanance I open the engine every once in awhile to check the internals... after more than 6gals the pitchs is pretty much gone but there's compression no scratches on piston or sleeve.
Xray NT1 '08 /'09 EC LRP12R / Serpent 720 '08 RB Concept V12, R3 RB mods, V12 Rody, Matrix RW / Serpent 733, 733TE RB T9 / EA RC8T OS .21 Vspec speed tuned / Kyosho Inferno GT, GT2 / EA SC10 / Serpent Cobra GT coming soon!