Minor update. I've been patching up the wing. I've tackled the surface rust on the top of the passenger wing - grinding down to good metal (and removing/grinding off someone's previous poor attempt at welding new metal ontop of rust) and then a good coating of POR-15. This wing is still on the car and i'll tackle the rest of the rust once i've got the wing off.
the drivers wing is already off the car and i've cut two great big holes in the side of it - it was completely rotton around where the side trim bolts onto, so about 3" square section has been cut out of it and a new piece of metal welded into place. As its my 1st proper weld job on the car i'm pretty happy with the result now its sanded down. I plan on treating the whole repair patch to a thin coating of POR-15 on both sides and then a little thin layer of filler to even it all out, then it should be ready to paint. Luckily the amount i needed to cut out didnt go too much into the wheel arch curve.
After i've finished this, i have a few other small bits of metal to weld in where rot has been cut out and the wing will be rust free.
i'm amazed by the thickness of the genuine MB wing. Its about 1.6mm thick.