ORIGINAL: bigtim
on the ones I have the connector is a nice tight fit with no slack, so far, if you notice the servo lead is loose in the connector junk the extension and try a new one.
The problem with this is that with vibration, heat, glow fuel, oil, etc. even a tight connector can land will et go.
ALWAYS use a secondary mechanism to keep the connectors affixed.
I've purchased some very inexpensive clips ( $.20 / ea ) from HC/HK, which I use on extensions that I undo all the time.
For more permanent extensions, dental floss, heat shrink tubing, knots, etc. are all better ideas.