The plastic impellers on the BMW E39 water pumps do exactly the same thing. They go right around 80,000 miles. Mine grenaded suddenly at 4,000rpm at something like 79,500 miles and the resulting spike in system pressure took out the upper radiator hose as well.
The radiator hoses have plastic ends with integrated seals and clips (not just hoses with metal clamps) and that is what broke. The rubber hose portion was fine.
While replacing the pump I also had the fan clutch replaced - they tend to seize up around 100,000 miles which can cause the plastic engine fan to explode and punch holes in the hood, tear up hoses and belts, etc. I also had the expansion tank and thermostat housing replaced since they are plastic and tend to crack and leak out all your coolant. The only piece still original to the cooling system is the radiator - which is mostly plastic and tends to crack at the sides and dump your coolant.
Gotta love plastic in a cooling system...
I've replaced the radiators proactively in both of my W123's to avoid this. The expansion tank on my turbo will be the next thing to get replaced. At least those are the only plastic items on these cars when it comes to the cooling system.