Thanks for the suggestion, but sadly doesn't seem to be the problem. It happens if I disconnect the GPS Unit, or if I manually enter the Lat and Long etc, it happens on AC power and Battery. It happens if I use a USB cable and use ASCOM and SKYCHART to control the slew. I dismantled the scope and took the large cog out and cleaned the (alt) encoders and looked to see if there was any obvious problems - still happens.
I haven't taken the bottom off and look at the Azi encoders yet.
https://youtu.be/uFou1a7adVQ
https://youtu.be/Kn1YvN2W1es