When to Change Expansion Tank?

[Georg300]

Hello,
My X5 has 91K miles, and I am trying to get things done before they break. For example, I am replacing the original water pump as we speak, it works fine but being the original, I decided to do it.

The question is about the EXPANSION tank. The one on my 328i cracked at 100K, is it because it was old enough? or some other reason? It was pretty hot that day, and I just had taken the car out of a shop for service on one of the rear bearings. Since then I have been using the stealership for peace of mind.

BTW, that time, the expansion tank had a huge crack, I mean the entire coolant went in a matter of one or two minutes, rather weird.

Should I replace it now? Also, what else is there? I am trying to take care of things that, potentially, could leave me stranded, so for the thermostat (for example) I will wait until it starts giving me weird readings.

I appreciate the expertise!