Fan motors are very easy to take apart and service. Once you've removed the fan assembly pry out the connector adapter and then take out the one screw on the end of the housing. The motor and fan cage should then easily just pull out. Clean it all out with compressed air and oil the bushings. You may find the brushes have worn and the brush wires have no more slack. A little work with a soldering iron can get you a few millimeters more brush wire slack that should resolve the problem for another year or two.

I did lubricated mine twice, which held up a few months each time, then finally decided to put in a new fan/shroud for about $140 ...

Here is how I did it. Once I had the assembly off the car (instructions on Volvospeed/Bay13), I put bearing grease on both ends of the motor, where the shaft meets the bearing. This is easy on one end, but the impeller blades are in the way on the other end. Because I could not figure out how to get the plastic impeller off intact, I drilled a hole in it, close to the shaft. Through that hole I was able to insert a stick or screwdriver with some grease on its tip. It takes 1-2 hours to get this done. There may be more appropriate grease than the stuff I used, and if so it might hold up longer.

It's all a matter of where you want to fall on the aggravation/time/car's life expectancy/money equation. In most cases, when I have tried to save money on stuff like this, it was a waste of my time. I bought my fan, as most parts, at FCP Groton (10% off with code JUNEBUG).
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'97 850 n/a Wagon, 170K mi ... '98 V70R AWD 106K mi