Replacing the rear main seal is a labor intensive repair, but I can't
fathom it would cost more than replacing the engine.
Check your oil level to be sure it's not overfilled. This can cause the
smoking you describe. The clear fluid and dark substance may be water and
carbon, which would be normal. The V6 engine in this car is known for
having valve stem seal leakage issues, and for sometimes dropping a valve
guide, allowing oil to enter the combustion chamber and resulting in smoke
from exhaust, particularly on initial startup or when idling for a
significant period of time.
None of these things will be cheap to repair (unless your oil is
overfilled) and may well approach or be more than the value of the