I use a Milwaukee MW101, and I was sure to get a bottle of Storage Solution along with the usual buffer solutions. The pH probe came with a silicone-rubber end-cap that is used to protect the end of the probe when not in use. The end-cap is tight-fitting and is intended to hold a small amount of storage solution to keep the probe tip wet during storage - dry tip = unhappy tip.
Mine always sits in its original box when not in use. Before putting the meter away, I'll rinse the probe tip in distilled water, shake lightly, check to be sure the end-cap has enough storage solution in it, install the end-cap and put the meter away. Simple, really.
Replacing the probe will become necessary only when drift becomes no longer manageable. Many pH meters allow easy calibration using one or more buffer solutions - I don't always recalibrate, but I do always double-check by using one of my buffer solutions - if it is spot on, no calibration needed. If it is off, I'll do a two-point calibration.
When calibration is no longer possible - it just won't settle near where it's supposed to and wanders all over the place - it may be time to replace the probe. This assumes you've kept your buffers in good shape. I've had my meter for about a year and a half now, and the probe still holds true each time I use it.