Oil filter cap
 

Gentlemen,

I have a 2008 Mercedes Diesel V6. Upon changing the oil I replaced the ring on the oil filter cap and tightened down. There seems to be a gap in the threads for the ring about two threads from seating directly to the cap. I tightened it down to where it felt firm, not wrench tight. It immediately started pumping oil out like a sieve. I took a cap tightening tool and really torqued it down but I am still getting some leakage. What am I doing wrong? Is there some spec to torque this cap down with a wrench and a cap-like filter tool?
The ring when tightened down FIRMLY gets distorted and small leaks occur. I bought the oil filter and rings from Mercedes Benz of San Diego so I assume I got the right parts.
Any help?