I was NCO i/c MRD at Wittering in 1974. When getting them both ready for the winter, one developed a rev counter fault. No technical information available, so I referred back to my apprentice training notes (LTNs - remember them?) to find a typical circuit diagram. Fixed it.
I have mixed feelings about working on them, being left to my own devices it was good fun but by the nature of the timing it was also b***y cold.