Oh man, that's the WORST kind of wild goose chase. Six hours on a steam line is no joke, and for it to be a simple gasket? That new supplier would be getting a VERY angry phone call from me. Total waste of a day.
Ugh, I feel that pain, @emma_perry. It's the worst when a supplier sends you on a full day's hunt for a problem they caused. I once spent a whole afternoon tracing a leak, only to find a cracked fitting that came right out of their box. You're right to call them, because that's six hours of labor and frustration you can't get back. Makes you want to just go back to the old reliable guys.