Whoa, thanks for the tip Jerry, copper crush turned up a treat, and affordable too. Ordered a pack of 1.5mm thick ones, they should do, old ones were 2mm. Arriving Monday.
Thanks for the gauge info Peter, the chamber actually seems to be holding up at 20 microns with the old gasket in the gauge, I've yet to check readings with the turbopump running though. Reading through those docs.
The more you get into it, the less mystifying the nuts and bolts of science hardware seems to get. From the outset it seems incomprehensible, but things simplify as you work on them. Point being it seemed to me at the start as if conflat etc had to be rigorously justified by in depth models and so on. In reality, the only model that looks like it matters is experience.