Oiling a PS fan is not a cure. If you fan needs oil once, it's going to require it again and again because a bearing is shot. That is if it IS a bearing that's the problem. More often than not, it's a brush that's failing. In that case, no amount of oil is going to fix it.
It's true that debris could cause you some of these symptoms and that blowing it out could do the trick. The way to determine this best is to blow the compressed air into the blades while you're cleaning it. The if the fan spins really well from your compressed air, then it isn't the bearing or debris, but a brush that's the problem.
You could always replace the whole PS, but most fans are just plug and socket and yes, if you need to replace you could cut the wires (usually black and red) about midway and strip it back some (as was already suggested).
I've seen this type of thing hundreds of times and usually any performance problems with any fan in a PC usually requires replacement. If not immediately, eventually. Unless you have a lot of dust buildup and still that sort of thing will have a bad effect on the best of fans and could take it out too.
Carl
