Today I pulled the mast on O'Day 34. I knew one of my mast head sheave was gone because I witnessed the parts come showering down on my head last year from my bosson chair. When I removed the cover plate to inspect the sheaves - there we four sheaves intact - the two forward pair, a center pair that didn't look like they were supporting anything then the axel for the rear sheaves which the rope just ran over (since they were gone). What's really confusing to me is that it looks like there's only clearance to fit a roller into the slot (it's only 1 1/8" wide). The sheaves listed for this mast on RigRite's web site are all 2" or larger. The carry a delrin roller which they say is for an internal spinnacker halyard. My spiniker halyard is externaly mounted though. Has anyone out there run into this. Are the main sail and jib halyards supposed to run over a roller on the back portion of the mast head? What's the second set of sheaves for (between the roller and the forward sheaves)? See below link to RigRite's site for this mast.