Thanks Middy and Dennis. Yep, I've eliminated all those issues... still have the problem.
Thanks for the advice though!
Now that I've learned how to process in K3ccd (done it once!
) I'm keen to maybe have another DSO attempt and see if I can subtract my darks with K3... just to try something different. If the problem persists at least I'll know it isn't software related.
Al.