I did mine and its the first auto trans I have ever had apart. They are really not that tough. One of the clutches I had problems getting the spring retainer off and actually broke one(had a spare) because I thought I could do it without making a tool. Made a tool, had a buddy help me and used an arbor press. Other than that I had to make a deep well 30mm socket for the rear flange.

I also rebuilt the one in my 420(same trans) it took me about 8 hours start to finish including R&R.

If it has more than 200K on it, at least one of the clutches is close to being toast.

Trans X is just a band aid, at the amount of miles these cars get to the trans is just worn out. What other car will go 200k+ without a trans rebuild.

You will be into parts and everything less than $400.

Get a banner kit with all the seals and clutches, cost is ~$200

Find a local trans rebuilder that rebuilds torque converters and have them rebuild yours while you are doing the trans. Mine cost $150

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81 300SD daily driver/project
86 420SEL (sold)
85 380SE(in the graveyard)