I would suggest that you replace all three rubber air cleaner mounts, and ensure that it is on correctly and connected to the crankcase drainback line properly. Also be sure that you check to see that the seal in the bottom of the air cleaner is in good shape and fitting on snugly. These parts are very important for long engine life, and very cheap.
The Napa filters are good quality and they do provide the filter for this engine.
Enjoy your new baby and keep us posted.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in