Dirt in windshield wiper fluid can plug the pump or nozzle.
 

I checked the wiper fluid reservoir and saw a lot of dirt. Pumped the fluid out, cleaned the reservoir in and out. Put back the fluid filtered thru a kitchen paper.

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An el-cheapo in-line fuel filter (see through is nice) can help keep your nozzles from getting clogged.

Not a bad idea, the fuel filter can be connected after the pump I guess. Has anyone done it?

I learned that "trick" from a German MB mechanic. He uses it on all of his cars, including the 280SE that he sold me. (The 108's and other, older models, use a rubber bellow to squish the fluid through the lines to the nozzles - You don't want crud to build up in those bellows, because over time their holding capacity gets reduced and what used to be a powerful stream, turns into a trickle. (besides the nozzles getting clogged).