The hissing, I had the same problem on my 94 acclaim which goes through 5 tranny rebuilds in it's life time. (10 years no more)
The hissing there came from the torque converted falling apart, and metal stuck in the filter from falling apart moons or orb moons or whatever they call it.
I gotta say that this is very surprising on a 190E, I hear those transmissions outlast anything else in the car, so you must have been driving it real hard, or not changing the fluid in the tranny.
I got an 85 190E and my tranny works like a charm.