Replacing a rotted boomkin

I’ve discovered that the joints at the end of the boomkin have rotted. My boomkin is different than most and consists of two arms with a third piece parallel to the stern that connects them with top and bottom stainless steel plates holding the butt joints together (two backstays, one at each corner). They appear to be teak or mahogany (the rest of the external wood is teak). All surfaces were painted before they were assembled but there is no sealant at the joints or between the arms and the deck. Surprisingly, neither the arms on deck nor the deck itself showed signs of rot. There are four bolts through the deck on each arm, with no backing plates under them. Given the cost of Burmese teak, I am replicating the boomkin using Honduran Mahogany and have a few questions. I invite your opinions.
(1) Although the construction manual calls for 3m 5200 between deck and wood, I plan to use Sikaflex 291 both on deck, between the joints, and between the wood and stainless steel plates, given the removal problem for 5200.
(2) I am considering using Cetol rather than paint on the wood primarily because future rot might be more easy to detect, although paint would be more protective.
(3) I am thinking that there may be no need for backing plates under the deck since the stress is primarily horizontal and no backing plates were originally used.
(4) I’m planning to re-drill oversize holes on deck, “keying” them with a Dremel bit, filling them with epoxy, and then drilling new bolt holes to reduce the likelihood of future rot in the plywood under the fiberglass.
Any input would be appreciated!

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