w115 220 Tranmission dead

I have a 1972 220 Auto that's been parked for the last 4 years, waiting for me to weld new sills. This weekend I had to tow it about 30 km, in moderately cold weather (really cold for those not from
Scandinavia). The engine will run, barely, but there is very little power, probably due to a stuck distribtor advance or the carburettor. I topped up the transmission fluid, and let the car run for 10 min before the towing. When we stopped towing, there was smoke coming from under the car, it seemed to be from the transmission, and the smell supported this...
After an hour of cooling I started the car. There was loud rattling sounds coming from (probably) the transmission regardless of the position of the gear lever. Still, the car would move, and both reverse and drive seemed to engage in a normal way, there has always been a delay of 1-2 seconds when enaging reverse.
Any idea, anyone.
Arne Falch Oslo Norway.
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