Youy don't want to seal the claps. They need to breath...to allow moisture to pass through the wood.
I highly recommend against any film-type finish. Stick with a stain, from transparent to semi to even a solid stain.
Solid has a paint appearance, but it still more permeable than a paint.
A concern is what it on the claps now? That may cause you to lean one way or another when it comes to re-treating the siding.
A lesser concern...claps are milled with a smooth side and a rougher side. Do you have the smooth or rough (more wood grain, crevasses, etc) showing? the rough side is better (more tooth) for more heavily pigmented coatings like solid stains.
You have freedom to do as you choose, but existing conditions may make one option a better choice over another.