In reply to Xharlie:
PU is polyurethane and in tents used to waterproof the fabric.
The white waxy stuff is the PU coating letting go. Leaving just a woven fabric behind, which explains the leaking. Some PU coated fabrics suffer from this issue, sometimes batch related. I have had fabrics from the same company, one started flaking really soon, while the other kept on going for a decade before I tossed it because of a broken zipper. Next time, If you see it start, I would suggest to contact the manufacture immediately. It’s a manufacturing defect. Not sure what black diamond will say if you used it for years like this. But you could try.
Unlike silicone, you can’t apply PU on a fabric without special equipment. So there isn’t a good home fix for it.
I don’t own tents which are sold in the UK or Germany. Although I did noticed the Aldi tent being pretty nice and durable (for basecamp use that is), especially for the price.