To answer your question, it was the gears in the overdrive unit that were seized, and yes, the car did run for many years. Not well, mind you. Transmission was crap with a dicey second gear anyway. It was on the list of things to do--after one last 2 day tour trip
Second, there was increasing vibrations followed by a BANG! and then some black smoke, and some extremely bad vibrations after that. At that point, a mile or so from my host's BBQ, a very slow crawl was done to get it off the 4 lane, followed by a tow to a shop to drop the transmission out (about $500 there). I came back with a Jeep and a dolly to pick up the car, and tow it for 5-6 hours home, with the transmission out. ($300 just for that roundtrip--the Jeep sucked gas and the $60 in tolls didn't help) The transmission was taken about 1000 miles by me on my next 750 mile trip to central Canada--so only a detour of 500 miles round trip from Ottawa, to drop off at a specialist oldtimer expert. 3 months and another $1300 later, I reversed the process and picked up the completely rebuilt transmission+overdrive, and then paid to have it properly re-installed
So, don't ignore the problem!!!!