Nevertheless, after 17,000 kms, this chain hardly shows any wear other than some cosmetic polishing. It has no stiff links, and there's a consistent mild resistance when bending the chain (as in a new chain), indicating that the Z-ring seals are all still good. Here's the outside after cleaning with mineral spirits:
And here's the inside (left) and outside (right).
My maintenance ritual has been a daily brushing with a nylon motorcycle chain brush ($10 online) to remove trail grit, then spraying with a paraffin-based chain lube while the chain is still warm from riding. The paraffin builds a tenacious Cosmoline-like layer on the chain that repels water-blasting even in heavy rain. This routine has rewarded me with no significant wear of chain or rear sprocket (a Dirt Tricks sprocket--awesome quality), although I've had to replace several front sprockets which is to be expected. Previously I used Dirt Tricks front sprockets, but when I was not able to get a replacement in time, I thought I'd try Renthal sprockets at half the price, and was pleased to see a good 8,000+ km out of one before it needed replacing. I'll probably stick with the Renthal counter sprockets from now on, as they are cheaper and more easily available, and I don't see a significant wear or running advantage over Dirt Tricks.
Dirt Tricks has a great guide to measure your chain wear. I didn't want to disconnect my master link, so I measured 50 spaces between pins and got exactly 31.25", which is exactly half of the 62.5" you should measure for 100 spaces on a brand new 520 (5/8" pitch) chain.
I was surprised by the lack of chain wear and at this rate will likely get another good season out of it before it needs replacement.