My 1985 300D has ~330K miles, but a new transmission was installed ~220 K miles by the prior owner. Mine is the CA model w/ the 1986+ transmission, but I also have a 1984 300D. I have kept my eye on rebuild kits and they are pricey ~$380 for one w/ all seals and clutch plates, and I think that doesn't get you the B2 piston or modulator. They also look intimidating inside (youtubes) and I wonder if the large nylon part (not in kits) ever gets brittle. I'll file away the PN's.

I compare that to my Chrysler transmissions I rebuilt (FWD 3-spd torqueflite and 4-spd electronic), which were very straightforward (detailed manual) and took no special tools other than large snap-ring pliers. The rebuild kits were ~$100 w/ clutches. My three 1960's Chryslers are even cheaper. I got full rebuild kits for ~$50 it they ever need it, and same torqueflite design as the 3-spd I did.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans