A few days after I picked up our Cali I did a 15 minute hose test, left it a couple of hours and zero leaks.
Stayed over in Brighton a couple of weeks ago and had about 25 mins of quite heavy rain and a fair blustery wind. Again, no leaks at all.
Last night was fine rain, almost a heavy drizzle if you like. Just pitter-patting on the roof. Wind was very gentle (the wife’s Crocs didn’t blow away from under the van and my Rainbow Shades thermal screen cover wasn’t flapping at all). But the drizzle lasted hours and soaked the bellows. This, IMO, is key. They need to be soaked constantly for hours.
The seams on the bellows are thick and appear to absorb water, then it has to go somewhere and just leaks through. I have no noticeable pin-holes or stitching errors that I can see. When we closed the roof the seams squeezed water out like a sponge - that’s what’s stained the pop-top ceiling I think.
When we removed everything to dry it out this morning, it was evident that virtually every seam had leaked - front, back, sides. Horizontal, vertical. Even the rubber seal along the bottom leaked - although that was just the front area.
These 04S bellows do feel different than the 03S ones we had - thicker and a silkier finish inside. But evidently VW are not testing them at all - we are.
I‘m just reporting my own findings with my own Cali - I’m not trying to worry anyone and hope others with new bellows/vehicles are fine. It could very well be that mine if just a Friday afternoon van.