The teak seating surfaces on Beneteau's are a continuing maintenance issue.
The panels are comprised of a marine plywood backing plate with teak strips stapled & glued to the plywood backing. The plywood backing is then glued to a recessed area on the seats. Finally, a black caulking compound, such as boatlife, is used to seal the spaces between the teak strips. Assuming that your teak can be refinished, scrub it, treat with two part teak cleaner, and sand lightly to a smooth surface.
Do not sand too aggresively or you will expose the staples that help to attach the strips to the backing plate. If the caulking has deteriorated severely and the teak is OK, use a utility knife to score the caulking and remove it with the aid of a router or dremmel tool, mask the teak and apply new caulking. Finally, seal with your favorite sealer or varnish.
I use Semco teak sealer. It is simple to apply. No need to mask; just apply with a narrow brush and wipe the overflow from the black caulking and gelcoat. Usually apply 3 coats each season. It seals & waterproofs and leaves a non slippery surface, which is important. It doesn't look as good as varnished surfaces or cetol coated surfaces; however, much easier in my opinion.
Certainly, covering the seats with sunbrella fabric would preserve the teak & sealers.
With regards to the missing teak on the swim platform, your options are to fabricate a teak replacement or order a replacement from Benteteau. Some of the new synthetic products mentioned by Sail SF would certainly be a long term (hopefully maintenance free) option also.
