The dealer wont help you. You will need to buy aftermarket special bolts from Rad bolts in a 12mm shank ( so they will fit into your existing drums) and 14mm ball seat so they will fit your new rims with the larger holes. Bolts are about $2.50 each.
I have 2005 E500 sport rims on my 1990 300CE with these bolts and they fit fine
I have 2005 E500 sport rims on my 1990 300CE with these bolts and they fit fine