I had an old pair of JBL 212's with the sub given to me. I changed the capacitors to new Sonus (I think they were called) capacitors. They really sounded great - big difference, so much so that I regretted selling them.
Capacitors don't wear out but the newer caps are much improved. Swapping out the older for newer caps is not a difficult job, just remember to label the speaker polarity.