Time for an update - the new nosepiece arrived on Friday and fits perfectly (M57x1 thread). They also sent a new gasket that looks a bit more substantial than the original one.
Ran the camera at -15C all night last Saturday without any issues.
Clouds rolled in early this week so I haven't had another go but things are looking good and I'm pretty confident my troubles are now sorted.
The takeaway from all this for me is I'm glad I purchased the QHY8 from Theo as he made all this happen. Trying to ship this camera back to China on my own would have been a nightmare.
My experience confirms what others have said about Theo's excellent support.
Thanks for sorting this out Theo
