The only question I can come up with right off - Did you use another wrench to counter the force when tightening the fitting? If I remember correctly, the filter element has the flats to use a wrench to counter hold. If you didn't counter the tightening pressure you likely broke the fitting loose, causing the leak. If you did counter, then perhaps the fitting isn't tight enough.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.