Have solved it...for whatever reason a stop peg had rounded off inside the servo, and although said motor is covered by warranty, freddy fat fingers ere stripped it doon....there is a black spring holder in the center of one of the gears...this is what helps keep the initial position...this has a jutty out piece that should lock against the outer gear and it was rounded, why was it it rounded , i'd guess that the zorst flap being seized made the motor try to pull and someting plastic gave way..tis now trimmed with a knife and works a treat.
..it appears my Europe trip was with zorst flap open ...returning avg 56mpg, albeit a bit erratic at slow speed ...
Pash.. your correct if the unit has not had some kind internal failure or gear slipage...
If any one has a similar problem dont bin the servo it's may still be servicable..if you want indepth instructions pm me....that said the goal should hopefully bin the standar zorst get rid of the servo and
smile