The average time seems to be 5-8 years, although some have lasted longer with good care, and some shorter with bad. What typically causes burner failure is clogs in the holes of the ceramic plate. With proper use like waiting for the grill the get to temperature before adding food, and proper maintenance such as doing the 5 minute burn off on high after each grill use, the holes in the burner ceramic will stay clear for much longer. Waiting 3 minutes for the grill to get to temperature will prevent any liquid dripping from food from merely getting absorbed by the ceramic and weakening it, and instead it is burned up from the heat. The 5 minute burn off at the end of cooking sessions helps remove any debris on the burner by burning it away. This will also help keep your grates and your grill in general cleaner as well.
If you want to clean the burner more thoroughly, do not get the ceramic wet, as this will weaken it and make it prone to cracking. If the ceramic cracks, it will render that burner unusable and if attempted to be used, it can cause gas to build up in the burner before being rapidly combusted. Use something like a cotton swab or other dry, gentle, and thin objects to clean out the individual pores if they become clogged.
Unfortunately we cannot offer replacements for just the ceramic as improper installation will cause problems similar to the ceramic being cracked. The entire burner would need to be replaced, which fortunately is much easier to do. To replace a burner, it only needs to be lifted out and the replacement sat in. There are no screws or anything, it's plug and play.