An oil repellent layer is applied to either the surface portion having grooves thereon or its opposing surface in {TAIL ~ the vicinity} of {HEAD ~ the narrower gap} 
An oil repellent layer is applied to either the surface portion having grooves thereon or its opposing surface in { TAIL ~ the vicinity } of { HEAD ~ the narrower gap }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD