I've been using the MSR Whisperlite primarily to melt snow for the past 6 years. In that time I replaced the pump O-rings with the maintenance kit once - but I'm not sure it was necessary. However, after at least 60-80 mountaineering trips the pump starting leaking fuel on a pre-trip check. It turns out the plastic body cracked at the threads underneath the brass cap where the control valve is installed. If I had to guess, this could have resulted from over tightening the brass cap, hitting the control valve on something really hard, or from using it as the leverage spot to unscrew the pump from the bottle about a gillion times. Who cares - gear doesn't last forever. I can't believe how much use I got out of mine before it died. Plus, it has always been an excellent (liquid gas) stove. So, moral of the story - good pump, great stove, check your gear before you go - especially if you abuse it like me.