i did have an issue with mine a couple years ago , the passenger side was ok , but the drivers side barely sprayed to the glass...
i just pulled the rubber hose off , stuck the air blower in it , and it blew a pile of crap out of the nozzle...mainly polish i think.

everytime i go and get an oil filter or something from the dealer , i grab a couple sachets of the windscreen washer additive, they are only a Dollar each and they normally just have them sitting on the counter..
never had a problem since..