Some of the 'crud' may also be crumbling rubber!
For a long time, I had no complaint with the performance of the rubber-bulb footpump in my '72 250, but after so many years the rubber can deteriorate. If the bulb doesn't crack and leak first, the insides may start to crumble, spreading tiny rubber particles through the washer system to repeatedly clog the valve and nozzles.
I wound up wiring a small Delco electric washer pump, from an '80s Chevy Cavalier, to the circuit at the pedal switch that normally cycles the wipers when the bulb is depressed.
I did have to disconnect the wire for the wiper cycle feature, as I didn't add a diode or relay circuit to prevent feedback into the pump when the wipers were switched on, but that was a minor issue compared to gaining a reliable washer system.

Happy Motoring, Mark

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DrDKW