[cool68]

for extreme stuff like you are talking about will need to use a putty knife, and wire brush to knock off as possible. Use gloves, eye protection, long sleeve shirt with a old tarp or something on ground to catch junk. then go to NAPA auto parts, or someplace, to get commercial undiluted non-aerosol Gunk grease cutting liquid. there, or at garden supply store, get a hand pump pressure container to pour cleaner into. soak trans, scrub with brush and spray again. then if you can, use hot water to wash down. repeat process. no fast and easy way to do this. I never have found a commercial place willing to do this, only if it was a semi. leaks usually from pan gasket.
if you pull pan replace filter along with all fluid.