It's a long story, but I just changed my MB filter and orings. Upon close inspection, they all had a tan/brown bit of paint on them and generally this means Viton in Europe. We used to ID orings here in the US the same way, but not for 10 years or so.

Google "Viton" and you'll find: http://www.dupontelastomers.com/Prod...iton/viton.asp

It's all-around a superior product with both a higher service temp and chemical/acid resistance.