Black streaks

As every caravanner knows one of the most annoying thing on your van are black streaks, I have been caravaning for around 30 years and seen many leading products advertised to remove them but in my personal experience have found them poor and have ended up using a cream abrasive. Yesterday I gave our 2019 Coachman 675 Laser a bath, because the van is on a slight angle from left to right the o/s gets a lot of black streaks and the roof gets very dirty.  I can say that i had a ureaker moment and tried Blue magic, its a cleaner from ideal world tv shopping channel. We use it at home and with great results. I Can honestly say it is a fantasic product that removes everything from moss, grime and most of all the black streaks disappear our van looks like it just rolled of the production line.Has anyone else used this product and experienced the same results?. I am sure that at the moment they are doing a great deal on Blue Magic so now may be the time to try it. Does anyone out there use a product that actually removes black streaks and if so how much does it cost as i would like a comparison 0n price.Thanks now all we need is to safely come out of lockdown and get to the open road.