prepping old chamferboards?

we're finally getting our house moved so we'll be able to start working on it soon. The front has quite a few chamferboards that need replacing but I want to keep the side ones to keep costs down. As the photos show some have damage to them, possibly a combination of weather exposure and overzealous pressure cleaning in the past? What sort of filler would be best to use on this damage prior to painting? I dont want to spend money on filling it in only to have it fall out 6 months later!

Prime first then use automotive body filler. These are polyester based. If the defect is large or the wood rotten use a preservative and an epoxy such as selleys knead it or Builders bog.

The body filler would be the cheapest - try supercheap

Cheers
Pulse