check around valve covers for leaky valve cover gaskets, next check your oil cooler seal behind your oil filter at the block (known for leaking) then after that also check where your trans bolts to your engine, my trans's pump seal was leaking pretty bad and at low rpms there wasnt enough pressure to keep 5th gear properly engaged and burned up my 5th gear! When I finally replaced the trans the smell went away with it. Any fluid there could be oil (rear main leaking) or trans fluid (pump seal leaking)