Is the oil engine oil or transmission oil ?
you could have a axle seal leaking or front transmission seal leakng
ok I would have the mechanic that installed your rear main seal recheck it then, it could still be leaking
do you know if they removed the oil pan when seal was replaced , this is the correct way to do it , there is also a seal under rear main for oil pan seal.
I would think if nor rear main leakng you could have a valve cover leaking and oil could go into bell housing of transmission
I would still have them check it , to make sure after they just repaired your leaks
I would do that then have them show you what they see, just to make sure you see where it is coming from
that can smell bad
could be axle seal or or axle boot torn also grease on exhaust
does not take much to make smell on exhaust
that would be you best thing to do
Ok your welcome and good luck ,Thank you ROY!