I had the same exact experience when I put a Mann filter in my W202 last month. I even called up Phil and talked to him about it. It seemed TOO BIG. Just like you say. However the PN's matched exactly what was in there so I made it work. If any one ever told me they spent 45 minutes putting in an air filter I would have thought they were crazy but that is about how long I spent. I didn't break mine however. Another problem I found was that the cover is not exactly square so there seems to be an alignment problem on the outer corner closest the passenger seat. The "flange" is somewhat bigger in that area for some reason so you cant line it up the way you assume you should. That really through me off for a while. I finally took the under cover off so I could look up at the filter housing to see what the heck was going on. Long story short I decided to try a different brand next time.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra