RW32 1965-66 Canvasbacks, MNH Fine/VF Plate# Single Duck Stamp

1965-66 $3 Federal Duck Stamp (Scott RW32) showing a formation of Canvasbacks in flight above choppy surf. Illustrated by Ron Jenkins, whose clean lines and vivid sense of movement made this one of the more dynamic mid-century designs. This is a. Mint Never Hinged (MNH) example with full left plate number selvage (168790) and original gum. Slight stain lower left?