PH probe, cleaning, and life

[Gools]

How do I clean my PH probe? Is Vinegar safe to use on them? I have a little build up of calcium in the probes teeth. I also want to know how long these probes last. I have had it running since Aug/2004. I still reads good, I calibrate it every month, and it's usually dead on, but wanted to know if they are like light bulbs, and that they should be changed on a schedule.