Hi,
I reckon you need something more like a really fat ‘O’ ring or thick neoprene washer with a stainless washer outside it, so that you can pinch it up fairly tightly and get a good seal. I’m afraid I can’t give you a specific supplier though.
Regarding the reefing, I recommend slab reefing. Most cruisers seem to have this type of system and I can vouch for it working well. There are alternatives to a hook at the tack, but I use a hook system and it works for me. For the clew a typical Wayfarer slab reefing system would have a reefing line leading from a fixed point on or under the boom up through the cringle, back down to a block where the line turns forward and along the boom via a clamcleat or similar near the gooseneck end of the boom, finally turning down via another block for a comfortable angle of pull (i.e. straight downwards). This enables you to reef (and shake out a reef) from one position in the boat, typically on the starboard side (putting you on starboard tack whilst reefing). At last year’s Tidal Training w/e about ten boats with slab reefing similar to this each tried putting in a reef against the clock and as I recall everyone took less than 2 minutes from start to finish, some much less.
Mounting the aft block on a slider under the boom rather than rivetting it to the side of the boom allows you to make fine adjustments so as to obtain approximately a 45 degree angle of pull downwards and outwards, which is ideal, maintaining tension in the foot whilst holding the sail down on the boom.
You may want to have 2 or 3 earrings (small cringles) fitted between the luff and clew cringles to accomodate ties or bungees so as to be able to tidy away the portion of the sail which becomes redundant once you have reefed. (Don’t bother with any of these beyond about halfway back along the sail, as you won’t be able to reach them safely from within the boat when afloat.)
I hope this description isn’t too confusing!
Cheers!