Almost all fans were riveted when they started stamping them.Age and rust get to them.One with tight rivets and no rust jacking should be fine.I've seen fans fail on newer stuff dozens of times.I had one propel itself through the radiator on a 5 year old S-10 with 48,000 miles on the truck.Fans are a big seller here at the junkyards.They all can,and do break.I lost an aluminum one on my A pickup in the late 90's.That motor was well clearanced and would really fly on flat ground.I was flying flat out when I had a big crash,then quiet,with a huge vibration.Half my fan was missing.There were huge voids,or air pockets in the casting near the hub.It was never in a straight plane,but it didn't vibrate so I used it.It came from JC Whitney maybe 25 years before I put it on.I have no idea if there was more than one maker back then or not.