Its one of those things that is on condition - ie; is the core damaged, how much corrosion inside it etc. The only way is to front it up to a radiator bloke and get it looked at/pressure tested. I have had nothing to do with the all-aluminium radiators now getting around but from what I understand about them you get what you pay for. I couldn't ever imagine that an alloy radiator will outlast one made of stronger base materials though in the long term, especially with the right maint/care.