So I just got this UNI foam filter for my Puch Maxi (Murray). I don't know if it just wasn't supposed to, or if the carb for a Murray is different than a normal Puch Maxi, but it didn't fit. Not really even close.
Found this at Autozone that fits pretty perfectly, PCV valve grommet 42052:
Second pic is just with it on a little bit to test the fit, it will slide all the way on, and fits pretty tight.