This E46 M3 was suffering from rotten & corroded inner rear wheel arch panels (possibly due to mud collection). To do this repair we opted to remove the rear axle assembly so we could 'stand' in the wheel arch and access the area properly so not to miss anything. We purchased the genuine BMW replacement panels, and set to work carefully removing the old inner rear wheel arches so not to disturb too much outer wheel arch/wing panel or paint. Once the old panels were removed, we neutralised the metal & outer wing join with POR-15 Metal Prep which also coats the metal with a zinc phosphate layer to aid next level adhesion. Then we coated the rear of the new panels & hidden areas of the rear of the outer wing with a weld through primer so there would be zero bare metal left. Once the new panels were shaped, and welded in, and welds flushed, we could coat everything in 2 layers of POR-15 Rust Preventative Paint (the best rust protection paint on the market in our opinion). Then it was keyed to allow a coat of High Build Primer. Then sprayable seam sealer was applied in a high pressure low volume way to almost inject seam sealer into joins and panel meeting points. We also brushed seam sealer into the arch 'return' (which is usually where the mud collects) and shaped it so that water/mud couldn't sit in the arch return ever again. Then continued the sprayable seam sealer over the new panel to leave a textured finish and offer some sound protection against road noise entering the rear cabin. Then we finished with Body Colour Paint which in this case was Silver Grey A08, then a top coat of clear lacquer to offer protection, seal the paint & sealer, and allow water to bead/bound off. Then once inside the rear boot/cabin area we also painted the back side of the rear inner arch panel with POR-15 Rust Preventative Paint, and then finished the area with a decent amount of cavity wax. I think it's safe to say these rear inner arches will never corrode again. Then it was off to the bodyshop for them to professionally finish the outer wheel arch panel lips where the outside wing lip paint obviously discolours due to the heat from the welding.