had this exact same problem on a customers Lreg astra a few years back, managed to improve it a bit with several passes with the machine and some autosmart r2 which is now called evo fine but couldnt remove it totally as i didnt want to go too deep and remove all the paint.
i remember suggesting having the bonnet resprayed and then i could seal it and wax it so it was less likely to do it again.
my mate has got an Lreg mk3 gti in red, didnt have this exact problem but i machined it sealed and waxed it back in december 07 and because he hasnt kept up with the sealant and waxing often enough its oxydised and now looks extremely tatty.
red is a pain in the arse for oxydation unless you seal and wax on a regular basis.
hope this helps,