Ian off ill? Just not good enough Shouldn't be allowed!
Is Brett the young lad on the counter last time I was visiting?
Seriously, I hope Ian is soon back, firing on all cylinders.
As I see it, communication with the supplier is the most important bit, with any problems such as this and the best course of action initially. Arc can decide/advise/agree on the best course of remedial action – likely a more cost effective route (if small parts actually needed replacement would to do it in situ) rather than returning the whole item to the supplier.
Unscrewing a knob, which appears to need no tools for removal, does not seem (to me) )to be any reason for denial of warranty!