What is the average life expectancy of a (nice quality) water softener? and can you clean the inside?

Use up or bail out the salt. Clean with a broom. A new toilet brush works good. Change your brand of salt. sounds like you'r using solar salt. Solar salt is very dirty. sticks,mud etc. Recommend Morton or other name brand. The pellet type salt is much, much cleaner. and will keep the problem from comming back.