Just to add minor notes to Pat McAneny's post, this new insert perfectly matches my old SN insert (identical to the SM insert) and absolutely looks far better in off-white. Being made of EPDM it will stand up to UV and will not chalk up like the originals. They're made by Techno Rubber Industries in Miami and I visited their plant for an "eyes on" - they're a family business that's the "real deal". You can Google them for a look-see.
Installation is easily accomplished with a spray bottle of water and dish detergent plus a blunt "pusher". I used a hand held 1/4" socket driver (without a socket) as pusher. Here's a pic - the tool is lying on the deck, but anything similar will work - it does take some force to work the inside edge of the insert down against the outside of the cap rail.
It will take you 5 minutes to remove the old insert - just pry up one end and pull - and about an hour per side to install the new. Amel carved away the bottom section of the originals in the areas of the chainplates and you'll need to copy that on this new one.
Before installing the new insert, I'd recommend taking the time to wash out the empty channel as it really accumulates dirt and then clean and wax the hull and rub rail, patching any gelcoat nicks you may have.
I think it will be a super improvement and Joel says to add 15% to your asking price when you sell. (Well, maybe not an exact quote, but, hey!)
Cheers, Craig - SN68 Sangaris, Tropic Isle Harbor, FL