I tried Googling this and nothing even remotely close can be found to answer your question. Personally I think over a period of time, it would start to leave marks - water marks, whatever, on the matte paint. Yes your paintwork should be protected by special matte products such as Swissvax Opaque for example, which will help to stop marks forming.
My suggestion to you would be to apply Gtechniq G1 to your windscreen because this makes it difficult for dirt / muck to adhere to your windscreen therefore less need to use your windscreen washer fluid. In all honesty, I have yet to top up my windscreen washer bottle since I've owned the RCZ, which is nearly 26 month old and 21,000 miles+ [shock horror !] (and I don't mean my husband has done it for me instead ...... Lol ). It really is a great product in so many ways - also stops ice forming on your windscreen too unless -6C or higher. Can usually brush it off with your hand and you'll save your wipers too. It's a WIN WIN situation
