Trevor - my deepest apologies, it seems I missed your reply back when I posted this. Thanks for the reply and info, sounds good.
Things are looking better on a few issues.
1) Whilst the focuser is slipping, it does only seem to be when the OTA is basically pointing towards Zenith. It does slip even with the Andrews 2" 80º eyepiece, which is NOT that heavy. Slipping isn't really an issue with the eyepiece when away from Zenith. The camera (Mark IIn) seems mostly OK as well now, at least from my experience over the past 2 outings with the scope setup.
2) My ability not to achieve focus seems to be only when using the WO diagonal. When imaging, I am now removing the diagonal and attaching the camera directly to the focuser. No further issues, focus achieved every time. Much happy am I!
Thought that I'd update everyone
Dave