Reply to Unresponsive jog wheel

Hey all, iv owned my vci 100 for around 6 months now but iv noticed that the left jog wheel is becoming less and less responsive. for example if i were to spin it backwards, the track in deck A would only move a bar or two. has anybody got any ideas to what maybe the problem? to my knowledge there have been no spillages so im guessing its not water damage. Any help or tips wold be greatly appreciated.
Thanks
Phil