Recently, I learned the bolts for my Invidia N1 catback exhaust had rusted badly and were splitting. I put the exhaust on my '06 MCS back in February 2010, so they were only about five years old. I'm sure the condition of them would be better if I still lived in Virginia, as we rarely had to use road salt during the Winter months. The German road crews lay down a salt mixture even if there is only a bad frost in the mornings. Recently, it was explained this mixture includes animal urine, and this is a major contributing factor to the rusting of parts.

Having looked at the underframe of my MINI previously, I knew some of the bolts had a whitish coating that resists the elements. I did some research and learned that BMW makes Inconel bolts, which contain NiCr, or nickel chromium. Some of the formulas used for Inconel bolts can handle temperatures up to 2000 degrees F and are highly resistant to corrosion. I also learned the nuts are copper coated to help prevent seizing.

The even harder part was finding the appropriate replacement gaskets. I spent a lot of time looking through various forum postings, and no one really had any references. I can only guess no one has had to deal with this problem as of yet. I was able to find this single article mentioning NAPA gaskets: https://www.northamericanmotoring.co...1-exhaust.html. It turns out these are in fact Walker gaskets and part numbers.

The Invidia exhaust consists of four gaskets, two each of different size for 2.25" and 2" inner diameters (ID). I realized the first two followed the factory flange size. The latter two were harder to locate here in Germany. The equivalent size for the ID is 51mm, but I also realize 52mm or 53mm would also work so long as the gaskets are centered up before the final tightening.

Bolts: M10x40 (10mm diameter, 40mm length), 11 62 1 427 586
Nuts: M10 copper, 18 30 1 737 774
Two primary gaskets: 18 11 1 170 941
Two secondary gaskets: Walker 31367 (or any 2", 51mm, 52mm, or 53mm equivalent)

The price of the bolts per Real OEM is > $20 each, but you can find them cheaper. I paid $11.82 per bolt. A couple of sites advertised galvanized bolts for $2 each with the same BMW part code. Do not buy these! They are cheap knockoffs. The nuts are $.70-1.00 each depending on what site you find them on.

German and American BMW part number databases sometimes vary, but the aforementioned numbers seem to be interchangeable between the two. If you need to know some German terms, try these:

Dichtung --> gasket/seal
Auspuff --> exhaust
Auspuffdichtung --> exhaust gasket
Innendurchmesser --> inner diameter


Condition of the bolts before I removed them (they appear darker because I had sprayed them with Liquid Wrench to help with getting them off, though most broke):




What the bolts, nuts, and two primary gaskets look like:




Bolting up the Invidia exhaust to the factory exhaust manifold with two of the bolts, two nuts, replacement gasket, and Anti-Sieze on the threads:




Two secondary gaskets and nuts/bolts tightened up: