I know an E34 535 muffler will fit a 525. I had to replace the muffler on mine... I don't remember where we bought the new one, but a note came with it that said that due to the complaints about the factory 525 muffler being loud (it was supposed to have a sporty growl) they have decided to use the 535 casing in place of the 525 casing, which does in fact make it VERY quiet. Now all I hear is the tickety-tackety of the lifters.Originally Posted by carsben353