Many thanks Martin and you ffejrxx.

All the gears check out okay, but I suspect the 'pot' may be the cause of this issue. I forgot to mention that these servos were not new when I purchased them from a mate, who assured me that they had hardly been used. He uses servos without their mounting grommets!! I'm pretty sure that the 'pot' brush/wiper would not like that, as the engine vibrations would cause bounce or hammering of the brush tips on the carbon track.
Getting a replacement 'pot' will be costly, so I will take this servo out and use it for spares. I see that in RCTech, many favour the Savox servos, so maybe that's the way to go for reliability.

Thanks for your tips guys.


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