[Derek Lecours]

The best solution is proper drainage.
I've done this by drilling a few small holes. There are a lot of little details I didn't include in the first posting.
Where the drill bit penetrates the first sheet of metal, primer and painting with a little brush is recommended followed by proper drying and hardening.
Your wax idea is good. The cavity protection spray I used is sold at the MB dealer (Part # A 000 986 33 70 10 ). It comes with a long nozzle which I tracked deep into those same holes and liberally sprayed every place I could find on that hood (bonnet).
Another product is by the Wurth company also of Germany, Part # 0893.081-A and is also a cavity wax used on Audis.
Our 'B' has a great application of cavity wax from the factory, but is mostly applied to the underbody, but we can always improve on it.
I've also done a lot of touch ups by brush with the same products purchased in a non spray form. Filling the trapped area with wax might work, but I won't chance it.
We live north of Montreal, and we live with 6 months of salt spray on our highways. I figure 1 salt season is equivalent to 10 rainy seasons elsewhere and I'm not too worried about the MB rust warranty because I don't know anyone whose ever collected, do you?

If anyone attempts to drill, you must stop the drill bit from touching the 2nd sheet of metal by sliding a mylar strip of insulation down into the offending cavity before you attempt to make this hole, you then remove the mylar strip after the hole is completed.
You could also use a step drill bit to block deep penetration, and you should also use a center punch mark to guide your drill bit.
There is no room for error when doing this drilling. I hope to get pics up for you soon. Derek