Hello every body need a little advise I have a friend with a 02 3500
that seems to be leaking oil from a canister on the front cover. took the canister off nothing inside .appears to have a vent tube going in to it. never leaked or used any oil till now . 157k on motor change oil regulary

 

It's the catch bottle, designed to trap byblow fluids and emptied regularly.
Some people remove them and let the oil drop on the ground.