For anyone searching for a similar issue.

This turned out to be my own confusion between "HOME" and "PARK" - I thought these were basically the same thing and although HOME was initially set correctly during the playing with GoTo, PARK and SYNC I managed to lose/corrupt the HOME settings. This meant it was using the wrong HOME when calculating the GoTo. I did not see that anything was wrong as it was parking just fine at that expected location.

I unparked the mount and re-performed the physical HOME process on the Mount (orienting the RA/DEC). I cleared all SYNC data and then re-booted the EQStar EQMOD box. This causes the EQStar EQMOD box to reset the HOME position to the current position. I then pressed the "DEFAULT" and "WRITE DATA" buttons in the mount PARK settings. It now works fine. Lesson learnt is that PARK and HOME are not the same thing and once the HOME location is no longer valid then playing with PARK and SYNC makes the problem worse and worse

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