Try searching the archives on ppbb.com - there are several posts on MAF part numbers. They basically say you should replace with same, but several versions are available. You may need to consult a dealer for the proper replacement.
http://www.ppbb.com/boards/ppbbphp/showflat.php?Cat=&Board=ARCHIVES&Number=863882&Forum=ARCHIVES&Words=MAF%20part%20number&Match=Entire%20Phrase&Searchpage=0&Limit=250&Old=6months&Main=863840&Search=true#Post863882
996 606 123 00 - original sensor- Bosch PN B3130-70627
996 606 124 00 - update 1 - Bosch PN B3130-128499
986 606 125 00 - update 2 - Bosch PN B3130-149265
986 606 125 01 - update 3 - Bosch PN ?