I agree that undue stress is the most likely cause. Consider testing the whole starting system, including battery. It takes a LOT of energy to start an engine, even a 3 cylinder. Starting systems are designed with MTBF calculated for 2, 4, maybe 10 starts a day, not at each stoplight. In a "normal car"

you'll get 5-8 years on the starter @ 3-4 starts per day. The battery will last 4-5 years if it's allowed to charge for 30 minutes after it's used to crank up. Yes, it can take 30 minutes to trickle charge from a 5-second start cycle. Why? The alternator's not designed to recharge 10-20 times a day every day, while maintaining spark and other demands.
This is why I believe that shutting off the engine does more harm than good (in addition to the heat cycle... water pump doesn't operate, temp spikes in one area, drops in another). It's all adding age to the car's components about 3-4 times normal rate. I'd expect some things to start failing after a year or two, yes.