I'm also missing it on the right cylinder.Excellent post! I'd like to know why I am missing the o-ring on the right head (removed head to install a timesert for the spark plug). In the left head, I found the o-ring in the hole above the nipple. The heads had never been removed.
Yes, each head has one around the aluminum oil restrictor.I'm also missing it on the right cylinder.
Each cylinder is supposed to have one, correct?