i am not knocking any cleaning products mentioned in this post, i have been around a long time tried many miracle products to my disappointment, then i turn to ecover truck wash not cheap but goes a long way and does the job, then ecover washing up liquid turns up brilliant for cleaning the glass, and hey brilliant for cleaning anything signs walls upvc theirs nothing i have not come up against that this stuff can not clean, but the most important thing everyone needs to know is elbow power is needed and the correct brush i have even found in worst cases i just soaked in pure water for 15 mins or so and the crap would just fall of, i just think that you should first clean with pure water first then see how you go from their if need assistance with any solutions, am sure you will find 90% of the time most crap will clean off easily with wfp, truthfully as ecover washing up liquid is cheap i just pre spray all before cleaning never had any issues as of yet