The only time you need to replace the quartz sleeve on your ultraviolet water clarifier is when it is broken. Even a hair-line fracture in the glass can allow moisture into the inside of the glass tube. That can short the lamp and/or power supply and cause you to have to replace either part or both.
Here's a simple method to see if your quartz sleeve is cracked and leaking:
Remove the lamp and keep the unit running like normal. Roll up a paper towel and stuff it into the open end of the quartz sleeve. Let the system run for a couple of hours (or you may notice instant results). If the paper towel gets wet - even the slightest bit - it is cracked and must be replaced.
Protect your delicate glass parts by removing the UV for the winter.