I've been commuting with Ortliebs on an OMM rear rack for about 5 years now, and have the same wear pattern on the OMM (about 0.5mm to 1mm). This appeared fairly quickly, in the first year of use probably, but doesn't seem to be getting any worse.
[EDIT] Took another look at the rack after posting this and noticed that one of the stay tubes was completely worn through on one side. So ... I'm now in the market for a new stainless steel rack
