Well, adding a drop of oil did some good, but I wonder how long it will last (one hour, one day, one week, one month ?). The fan I'm talking about has more than 45,000 hours of usage (and this is a relatively conservative number). It's a small 55 mm, 12V, 0.08A, 4000rpm+, dual ball bearing type of fan.
I also thought about adding a resistance to drop the fan speed. The only problem is that I don't exactly know which kind of resistance I should buy, nor do I really trust my electrician skill.
As for checking for old parts, I had no luck, and I don't intend to do exhaustive search anyway. I saw some, but it were overpriced.
And as for buying some non-fan related parts, well I don't plan to go this way, at least not for now.
The heatsink/fan looks like this:
http://www.dansdata.com/images/cel2/assembled320.jpg
The fan casing is specially made to "clip" into the heatsink. I might post a more relevant picture of it.