Well..............
It just gets more interesting - After taking the Reverse Y lead out of the system, I tried a few things, and it turns out the servo it dodgey!!!
A brand new Servo!! Its still doing the exact same thing, buzzing its way right to the end of its travel, then holding - then centering itself again??
I tried it in 2 other channel ports on the RX and .... same thing!!! must be the servo?

RJ