Masthead sheaves – If you are shifting to all-rope halyards, you will need rope sheaves rather than the wire-rope sheaves put in originally as they are much kinder to your halyards. Ken Pole's Santiva now has "three custom-milled Delrin sheaves from Zephyrwerks with brass axle holes. I'm extremely satisfied with the results. Sheave diameter and width were, respectively, 3" and 0.562" and the axle diameter was 0.432". My halyards are 3/8". Proprietor Ed Louchard advises measuring your own sheaves which he said can vary boat-to-boat. Cost, including shipping was about $105.00." Note that the masthead casting must be removed to exchange the sheaves, which means the mast must come down, the rivets drilled out and replaced with new rivets or tapped-in screws.
O-rings – This page, for O-Rings, Inc., will help you determine what size of O-ring you need. You can order from this supplier, but it may be easier to visit a local industrial supplier with the information found here. In Canada, Acklands-Grainger is an industrial supplier with outlets in many cities.
PSS Packless Shaft Seal – The Packless Shaft Seal is fantastic for keeping water from entering via your prop shaft, but it needs replacement from time to time (the manufacturer recommends six years, but Towser went 12 before someone mentioned this to her owner. Towser has a 7/8" shaft and a 1 3/4" shaft log, so the replacement part was PYI Maintenance Kit SP07-078-134R, US$105 with shipping from Defender Industries. Check Towser's dimensions against those on your own boat; they probably are the same but it's well to be sure