This varies by the specific model of wiper motor and the age. The later CW1 or CWX wore a finish of crinkle black (cover and body, although I've seen some with a crinkle cover and semi-gloss body). However, the earlier motors with the thin aluminum cover (with the vertical rib impressions) (CW3 I think) used a flat finish - your choice of gloss, but I prefer a semi-gloss.
Cheers,
Lew Palmer Registrar, NAMMMR |