The black plastic part which has a wire pluged into it on the rear of the transmission is the kickdown solenoid. Just forward of that solenoid on the side of the trans is the rear pump. It is not difficult to replace the seals, just watch for falling parts when you remove it.
Next toward the front is the B2 piston (I think). I haven't had that part off yet, so I can't help with it, but I'm sure that resealing it wouldn't be hard.
Back to the rear pump. It usually leaks at the round cover that is held in with a snap ring. Inside there is a spring and a piston. It can be very difficult to get the cover back in as the spring is very strong. Put the o-ring in the housing first, followed by the spring, the the little spring seat and then the cover. Press in the cover and hold while putting in the snap ring. It helps greatly to have a helper as it takes atleast 3 hands. There are an oil cooler line on that side of the trans which could also leak. Also check the dipstick tube seal.

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84 500 SEL (307,xxx miles)