Switching problem ?diseqc fault

[jex29]

I have a motorised dish.
I have been noticing a problem lately:

the receiver locks onto satellites when moving from E to W but not when moving back W to E. (However it always locks on Astra at 28E)
I have tried two different receivers and the problem occurs on both.

This seems to localize the problem to the dish/motor/diseqc.
As the receiver locks on a signal OK from E to W I assume the motor is positioning the dish correctly.

Could a fault in the diseqc switch cause this?

Thanks for anyone who can help

Jex