Engine Oil Leak

[Big D's H D]

Hi all, I just have a quick question, while changing my oil last week I noticed some oil drips and a stain from drips

running down, at what I'd call a bell housing inspection cap/plug (its metal and fits loosly like its a vent or something)

any ideas as to what this could be? The truck is a '09 2500HD FWD with only 19,000 on the clock.

The dealer here is not very good at investagating things, so if I have some info first about possible cause it would be a great help

Thanks in advance Dave

[govtech]

post a pic