Hi, was the dealer removing old fluid and refilling the reservoir on your dealer services? They used to on our fd. It used to annoy me as I used quality additives which worked better than the dealer stuff. But given the amount of clogged washer fluid lines/ filters I read on the forums, I now know why the used to do it. Check the pd log book service descriptions. I wouldn't expect there to be a problem, if they were flushing the fluid every service.
If I had to clean out the system i would get access to the reservoir via the front wheel arch (FD) disconnect the pump lines and push air backwards through the system. Inside the reservoir there is a small filter before the pump, which is usually the first to block up. Sometimes a jet of water into the reservoir can dislodge the scum. I DIY'd some plumbing fittings, taking mains hose pressure down to water filter diameter, crimped the end a bit with heat to make a spray that went perpendicular. I stuck that into the reservoir and blasted away at the filter area. I had a manageble flow out of the top and watched as chunks came away from inside the tank. I was lucky that the algee had not progressed into the lines.
