On my '89 420 SEL, a seal popped and I ordered the seal kit. When I got it, I called Auto Sports Unlimited in Zeeland, MI, and asked for a clean, dry box. Cost $60 plus shipping. http://www.AutoSportsUnlimited.com/
I recommend them only because I've actually been there and seen the back of the counter. Not too many places have their own rebuilding setup. I was impressed with the transmission case oven. Thery sell other stuff rebuilt, also.

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Gregga
'89 420 SEL "Moby Dick"
'30 Ford Coupe
'31 Ford Slant Windshield Town Sedan
'33 Ford Pickup
'34 Ford Pickup
'01 Honda Passport