i have a similar situation,
the wooden window frames on my victorianish house
have cracks, and are very rough where water has sat on them for years,
i was advised to wire brush them
then use car body filler to smooth them out
then paint with oil paint...
or should i fill the bigger holes with wood,
softwood would rot quicker than car body filler,
as its the frames they dont move like doors
so is car boddyfiller ok?