Drive shaft coupling was unroadworthy when I bought the car (most likely towing).
Gearbox went temporarily insane from day one (refusing to shift beyond second gear, stuck in some sort of limp-home mode). The problem was never properly diagnosed. Came good on good days, independent of when fluid was changed.
Some exhaust heat shields played like some sort of percussive trio depending on engine revs. Spot welded cracked bits together again; resolved the problem.
Engine light switched on and off on alternating days. Not diagnosed, but an old Ford mechanic pointed out some inconspicuous symptoms that meant the start of a blown head gasket (air bubbles in oil, on dipstick). No oil smoke appeared, though.
Engine occasionally refused to rev beyond 3000. Also seemed to be a limp-home mode set by the ECU. Wasn't repeatable at the mechanic, was temporarily resolved by disconnecting the battery and giving the car amnesia.
Diff had a whole lot of lash, but the car also did some towing. Diff sounded bad, but never actually let go.
I bought the car from some friends that have owned nothing but Falcons for the last decade and some. After I bought the thing, having owned nothing but small, aging Japanese sports cars and sedans, I started to ask them what they considered to be 'normal servicing'.
Cheerfully, they talked about the car's yearly water pump change, the two broken drive shaft couplings and brake rotors that were just as consumable as the brake pads. They seemed genuinely surprised that my 'antique' cars didn't need nearly this much care. This was just the Falcon experience.
Ridiculous build quality and unpredictability aside, it was actually a quiet, comfortable and powerful vehicle when it worked. I've had rental Falcons that were equally as nice, but that was the best thing about them; you could give them back before they got too comfortable in the relationship and let themselves go.
Got rid of it at bottom dollar because the stupid thing could never be trusted. This was the first and last Ford I'll own.