Kubota Digga wont slew

Hi guys I have a Kubota KX080-3 just rebuilt the engine and is running fine, all the hydraulics work great, drives back forward hi/ lo speed but it wont slew either left or right. It tries to and the engine loads up but no slew.
have tried looking for a manual slew lock but haven't found it as yet.
Any help would be much appreciated.

Kubota Digga wont slew