I have the Marving midpipe (from Spareshack) on my '05 S4R. The Marving has a mounting tab on the right side that bolts
directly to the engine, whereas the OEM midpipe/udder has a rubber grommet with bushing washers (to absorb vibration).
Well, the Marving mounting tab on my midpipe gave way to fatique stress recently and broke in half. Not a huge deal, as the pipe is secured at both the horizontal cylinder, and at the S-pipes.
I fabbed up two stainless steel "s" shaped pieces and welded them to the end of the broken mounting tab on the midpipe. I drilled and then filed holes in the mounting tabs to receive the OEM grommets and bushing washers. Here's a few pics:
I made a little too much space for the grommet and washers, but it'll work. Any aftermarket midpipes that bolt directly to the engine might have the same problem.