Grade 5 is what the factory used, in almost all general fasteners. I would surmize that the lock washer was imported garbage, not that it wasn't grade 8. GM used lock washers almost exclusively on fan bolts, but I have seen star washers used under the fan fasteners by some other manufacturers. I won't trust any hardware that comes from china. Id rather pick thru my used hardware, than to trust chinesium hardware.
You can fix that radiator with JB weld, as long as you get it dry, and clean, before applying it. Let it set up for 24 hours before filling the radiator with coolant. Your car, but I've never had an aluminum radiator repair fail using JB weld. I've used it on my own cars for fan damaged core tubes, and the car went to the scrap yard with the radiator still sealed many years later.
Some videos using JB weld on radiators:
https://www.youtube.com/results?sear...or+wit+JB+weld
