Dave,
Although I have never tried it myself (thankfully no odor problems from the vents of my car(s) yet. The "poor man's cure" is to turn the ventilation system on, then spray Lysol disinfectant spray into the air intake vents of the climate control system for awhile. There are of course, more professional solutions that your dealer or independent can do. But for the individual DIY'er, that is about the best I can offer for a quick job/solution.

Anthonyb,
Perhaps it isnt the leather but the padding underneath the leather. Try pressing down sharply on the seat then smelling for that "odd odor". The agitation of the seat should raise any of whatever may be down there causing the odor. You could take the seats apart, but from talking with Benzmac, that is a very large headache.

Hope this helps...Lee