Far as I know what killed most of the 500 sirens was rotator failure, either from the gearbox placement (oil sitting on top of a seal) or that damn belt that required splitting the siren in half to replace. I really haven't heard of any motor failures on those, most of them seemed to be the victim of politics.
I know from experience that the 10/12 500 is a BEAST of a siren, that really packs a punch.
https://www.youtube.com/watch?v=Rdh0O5nV5Jc