We have a Sears captive air water tank - unsure of how old since it was in the house when we purchased 8 years ago. We were recently told that the tank's bladder could be deteriorating because the tank needed air. We haven't noticed any problems with pump running more than usual. So how does one know if there's really a problem?
I received one quote thus far - plumber wants to replace the entire
tank to the tune of over $1,000. I looked at the Sears site and while I don't see a replacement tank, I do see parts. And the bladder is one the parts listed.

How does one know if the entire tank needs to be replaced, or just the bladder. I found a website that shows how a tank is replaced, but haven't found any sites that indicate the cost of a tank as compared to the bladder.

Its an enclosed tank so you can't "see" inside.