I am doing a refurb on my rear window aperture to clear up the rusty and pitted bottom ledge. Having cleaned it up to metal it is quite pitted and now that I have treated the surface I will give it a skim of filler before painting. However I have a couple of holes in each corner. Are these just perforation holes or are there meant to be drainage holes there? Photo shows the rhs with hole in centre of pic. Thanks
