I realise now why I've been burning them out...not asking a vital question (or reading the answer) a long time ago.

I've always thought that the RC valve spindle rotated anti clockwise to allow full power so I've been trying to set the valves up with the valve pulleys rotated as far 'right' as possible...when the servo has been trying to swing LO when turned on its been straining as it can't go any further LO on the cylinder...POP!

Honestly only just found out tonight (headbang smiley?)

Live & learn, not for the first time with the NSR