I washed with mine the other day and instead of just squeezing the dirt out in the rinse bucket, I squeezed it out then lightly rubbed it on the grit guard at the bottom of the rinse bucket. That took out some tiny chunks.
I'm gonna stick to just squeezing it in the rinse bucket from now on.
I see this happen more the older the Shmitt gets. Like anything else the material begins to break down over time. I've always felt I got my money's worth.