In the course of doing a brake job I encountered a couple issues. Any contribution from the collective hive-mind would be welcome and helpful.
1. Rotor cracks: The rear rotors had many tiny sub-hairline cracks. They weren't even visible till they got sprayed with brake cleaner. The dirty fluid revealed them. You can't feel them with your fingernail but there were a lot so I decided to replace the rotors. Anyway, they're surprisingly cheap, so why not? Now I just noticed that the front rotors, which seem to be in otherwise fine shape, also have a few of these miniscule cracks. There wasn't any judder or any other problem till my caliper self-destructed. Thoughts on replacing them too? I avoided because of fear of setting bearing runout.
2. New rear rotors fit perfectly EXCEPT..... they had an extra hole for a small flat top hex screw that locks the rotor to the axle flange. However, my axle flange doesn't have the hole for this screw so I can't use it as somebody intended. The screws weigh 5gm. I'm concerned that this small amount of weight - the weight that would otherwise be filling the hole in the disk - might be enough to cause a vibration cause the rotor is slightly out of balance. My plan is to grind the thread off the screw, put it in the hole and keep it there with the wheel. Does this make sense or am I overthinking it?