After driving less than 3,000 miles, I bent one of my 19" Cadiz wheels, but had it straightened by a wheelsmith. Since I never really liked them, shortly after the repair I purchased a set of 19" Advanti HY Hybris wheels--flow-formed and about 5 lbs lighter, running the stock 235/35 tires. In the 15,000 miles that I've ridden on them I've bent 2 and cracked 2. So my average dent/milage rate has been roughly about the same with both sets of 19" wheels. My winter wheels are from Advanti also, their Stelvio style. Flow-formed and light as well, the Stelvios are 18" running 225/40 winter tires. I'm yet to have anything happen with them, aside from a little curb-rash (I had them checked out last week just after having them removed for the warmer months), after about 8000 miles and 4 winters. And though the mileage on my 18" winter wheels is less than that on my current summer 19's, the potholes are at their worst during the winter months. My guess is that this difference between the two sets of wheels is mainly due to the lack of cushioning afforded by the 235/35/19 tires (3" sidewall height) compared to the 225/40/18 tires (3.5" sidewall height). 1/2" might not sound like a lot, but it's still a 17% difference--just possibly enough to bend or crack a wheel hitting a deep enough pothole at speed.
As per the OP, the crack in his Pretorias could have been started by the previous owner and only expanded to the point where there was appreciable air leakage through the crack over time. There's always those "known unknowns" that come along with buying a used car.
