When my low washer fluid indicator came on at the tail end of last year I was looking around for what fluid to use and people were saying that to be on the safe side and to avoid any issues with the fan jets to just use the SEAT supplied stuff. Obviously though it's not cheap compared to stuff you can get at the the local motor factors or online.
My car then needed to go in to VAG
dealer for some work and they kindly topped up my fluid at no extra charge so I didn't end up needing to worry about.
At some point however I am going to need to shell out any buy my own. If anyone knows of any tried and tested make/type screen wash other than the VAG supplied stuff that isn't troublesome with the fan jets then I would be interested to know what those are.