Rubbing greasy dirt where of the steerer against the headset bottom cup.
The sleeve which enlarges the steerer from 25.4 basic dimension to 26.5 for the crown race press fit is much longer than it needs to be, and the cup has been designed to clear only 25.4 on the reasonable assumption that the enlarged portion would be only slightly longer than the crown race. A bit of #judiciousfiling should solve the rubbing.
A bit of judicious filing should solve the rubbing.
I'll get the judicious file then!
Bit scary, but as you say it's only a sleeve not a structural part... Almost tempted to take material off the cup (If there's enough meat to it) rather than fork...
The sleeve which enlarges the steerer from 25.4 basic dimension to 26.5 for the crown race press fit is much longer than it needs to be, and the cup has been designed to clear only 25.4 on the reasonable assumption that the enlarged portion would be only slightly longer than the crown race. A bit of #judiciousfiling should solve the rubbing.