If the kegs are used, Id pull them all. Micromatic has the tool to remove the ring. They say you should replace them everytime you remove them. I think its BS. I use a phosphoric/ nitric blend in my keg washer instead of caustic, so I dont worry about beer stone. Id pull the spears if the keg leaks or the beer got an infection, but normally I follow the mantra.....if the keg aint broke, dont fix it.