Last night I installed the rockers on the head of my '89 190E 2.6. While tightening the bolts to the specified torque, one bolt gave that feeling that everyone has experienced, it was about to strip.

This was as it was close to it's specified torque. Question, Should I tap and put a helicoil in for this bolt? Are all four needed or is three enough?
Another question: Should I put antiseize on these bolts? I didn't think about it when I put them in.