My OEM cat blew a few years back - disintegrated from inside. This seems to be a problem with all BMW's, not just the ti. Good news is that we only have one - my 525 has 2, and I think four O2 sensors. I bought a BavAuto cat for replacement ($350 vs. $1200), which lasted for about 18 months and 12,000 miles. At that point it threw another code. They sent me a new O2 sensor to see if it made a difference. It didn't, so they replaced the cat and gave me a new warranty. I only had to pay shipping for the items, which was about $40. I figure if the cat craps out every 18 months and they replace under warranty, I am out only $40 and my labor.
If the BavAuto cat has failed for some on this post, you might want to call them and see if it's still under warranty. They were very good to deal with.
PS - consider buying the install kit also - it has new gaskets, bolts, and springs. __________________
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