i've used a 6" round "plate" air stone for about a year without problems, sterlized between crops & reservoir cleanings. the same reservoir has 2 of those small 2" air stones and they degrade and fade away after about 6-8 weeks. since you can get the small ones for about $5 for a package of 5 i just replace them as they chip and degrade.
I do not have this problem but I pump a lot of air into my setup.
I would be concerned what is blocking them. With enough air pressure they should not block. Are you changing the solution frequently, including cleaning everything regularly (I do mine ever 2 to 3 weeks)