On mine, i removed the back wheels(to get in the arch) ,sill ends and arch liners removed all the dry mud etc,
I noticed the lip of the arch has a bead of seam sealer round it which was not really sealing
with a sharp knife , I cut all that seam sealer out wire brushed everywhere, cleaned with brake clean so it was spotless,
treated any rust areas with kurust, etch primed,metal protection paint, re-sealed with plenty of panel mount ,some areas i did put a thick coat of waxoil
when dry refitted all panels , supertroled from inside the boot ,
I intend to revisit the arches in this dry weather to see what is going on and do a more thorough job including stripping out all the boot trim/carpet for access
also have a few bubbles in the near side rear door skin right at the bottom ,water has got in the skin seam
:
for some reason , this door on carltons, sennys and it seems omegas all start to rust before the others from what i've seen
(so whoever at Russelsheim is responsible for painting N/S/R doors wants F****ng with the fat end of a rag mans trumpet
)
I did treat it but 2 small 50p size sections are visible outside the door due to me putting too much paint on to protect it until i can use the correct matched paint (which I got to re-paint the front pro-drive bumper ,original CDX replaced)
I'd try and avoid drilling holes unless from inside the boot double skin areas and make sure it is 100% re-sealed