I think my best bet will be to 1)use a wite brush to remove as much of
the flaking paint as possible.
2) Paint the sill with "external grade, oil-based undercoat paint"
3) Repaint with masonry paint

Only one question. Where do i get this "external grade, oil-based
undercoat paint" from and does it have a more common name. Isn't
exterior gloss external grade, oil based paint. How would it being
undercoat, rather than topcoat affect it?