What's the best currently available paint combination for a new cedar windowsill in a non-freezing climate (San Francisco)? I've read that current oils no longer match the performance of their predecessors. But I also know that oil primers soak in to the wood much more than latex primers.
Here the old sill is a Marvin finger jointed pine sill, which lasted about 25 years:
The original sill was redwood installed in 1925, and all the sills on this side of the house failed (the rest are still in service). The location is shaded but not otherwise exceptional.
The Marvin sill will be hacked out, and a new redwood/cedar sill screwed in from below. I know the cross section of the Marvin design and know this will work (you can see the joint between the sill and the window frame in the picture).