The genuine item from your dealer should not be too expensive , and better quality than aftermarket parts .
I got a rear exhaust section for my 190E a couple of years back at a cost of £75 from the dealers .
Eurocarparts can probably supply an ERNST part at a reasonable price , I have bought these in the past and they are OK but not the same quality nor always as easy fitting as genuine MB .
Mark Cosovich ( the UK's leading W123 specialist ) may also be able to help (Tel 01792 846888 or 07714 089936 ) .