Just wondered if my wiper arms might need tightening or something. For a while now I can't get a good wipe. There are lines and little patches that don't clear totally. It is not the wipers because I have tried several new pairs over the last year or so. Mostly the Bosch aerotwin, but I have tried other brands and they all seem to leave the same areas. It is not the screen itself either because this has been well cleaned with different products as well. Was just thinking it could be the wiper arms themselves. Is this a common problem and if so, how would I adjust/tighten them? Thanks for any advice.