What was the outcome of this? I notice something similar, at similar mileage, with my PW-ST: the chainring moves (tilts) about 0.3 mm back and forth when one applies axial force at the teeth on opposite sides (for example by pushing and pulling at 10 and 4 o'clock). I was able to get rid of an accompanying creaking sound when pedaling by letting some oil soak into the right side bottom bracket (drive shaft bearing).