Cooling fan life?

What is the expected life of cooling fans? I built a system in June 2005, and it seems 2 of the fans I used have gone on the fritz.

The CPU cooler fan, part of an AC Freezer 7 Pro cooler setup, is making an odd "clacking" sound. I took a peek inside and found the fan "wobbling" in and out as it spins, making the odd noise.

While I was in there, I just happened to notice that my rear case fan, an Antec 3-speed 120mm fan, had completely frozen up! I tried turning the fan by hand and it was VERY difficult to turn. Bearng must be shot. The center of the fan was also very hot! I shut down the computer immediately for fear of something catching fire.

I suspect the CPU fan's bearings are also the issue with that one.

I have replaced the rear fan, and now I'm considering just throwing the OEM heatsink and fan that came with the Pentium D processor (still have it in the CPU box, never been used) along with a bit of Arctic Silver 5 that I have on hand. Money is pretty tight right now (baby on the way real soon, I'm the only one working), so I'd rather just use something I have than having to buy something new.

Anyway, I was just wondering if 3 years or a bit longer is the normal expected life of a fan that runs nearly 24/7.

Fans generally last until they fail. That's helpful, isn't it?

I have one system that has been running constantly for more than four years with no sign of fan (or anything else) failure. OTOH, my computers do not sit on the floor and I never use fans with sleeve bearings.

I do try to clean out my case, at least 3-4 times a year actually. It's a LARGE Antec case, probably 30" tall, so it kinda has to sit on the floor. It's just too large to sit on top of the desk.

I just ran out and bought the only 120mm fan Best Buy had, some weird RocketFish brand or something. It says it's ball bearing w/ 50K hr life, which is 5.7 years. We'll see.