It may actually be leaking from the back fo the intake manifold which is a common problem because of the design of the 5.OL block. Take a flashlight and check the back of the engine on top of the transmission and see if you can spot any wet fresh oil. My car has a large intake manifold leak that i'll have to fix, and i also get smoke through the shifter as well. This can also be caused by oil running down the exhaust to the catalytic converters or actually from running on top of the transmission and baking. Good luck,
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Mustang Parts Specialties ripped me off, it could happen to you as well.
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT