My first Volvo was a 1989 740. The ECU (LH 2.4?) did fail once, as did the air mass meter (as Volvo called it then) and the overdrive relay.
Piston slap was a reality, but it never did any harm. I saw the engine with the head off at 309,000 miles; yes, the cylinder walls still showed factory cross-hatching! A valve spring had broken; it needed a new valve, guide, seals, springs, and a quick clean up of the valves and seats to get it running again. The rest of the car was getting very tired so I chose to move to something else, but the shop bought the car from me, repaired it, and sold it a few months later. I actually saw it advertised for sale a couple of years later with 360,000 miles on it.