UPDATE - NO MORE SHUDDER !!!
Afternoon all,
I just wanted to give you an update - we engaged a local Auto specialist to undertake a "mega flush" and full inspection. The mechanic completed the flush, and we also opted to change to a metal sump to make future oil changes simpler.
We took the Disco on a decent 2hr highway run this afternoon and there is now no shudder at all. The mechanic told us this was a very common issue, and as we had caught the issue early there was very little chance of any damage being caused.
So despite some on here suggesting immediately replacing the TC, or even rebuilding the entire gearbox, a simple flush and she is good as new. We will now undertake trans oil changes with every service.
Hope this help others out there!