I've had mine since the very first Apple Watch and it had been on every upgrade until Series 6 graphite came out.
But last year with it on the S5 it started to get a few scratches. Up 'til then it was pretty much bomb proof, I'd knocked and scuffed it many times with not a mark on the band. But all of a sudden I started noticing scratches, mostly on the external of the clasp .
I'm thinking the DLC had slowly worn over the years until it's integrity against scratches failed.
I bought the SB milanese to use whilst I tried to source a spare clasp but the S6 came out before I found one and I went with graphite (with milanese) as SB wasn't an option (apart from Hermes). I still keep an eye out for a 2nd hand mint SB clasp as I still have the S5.