I think it would be better to try soapy water rather than chemicals that may be detrimental to the acrylic of the windows. Before you try any chemicals it would probably be a good idea to try a test patch on a piece that wont show too much.
------------- 'A sure cure for sea-sickness is to sit under a tree'
Solvents /petrochemical based products of any kind should not be used on acrylic windows as they could damage them. Try autoglym glass cleaner which is suitable for acrylic windows. A VERY FINE paste (farecla G3) may do the job without scratching the window, could also try detailing clay avaiable from motor accessory shops.
Just a thought,i was getting a sticky substance on the car windscreen for a few days at one time.On the news they said some volcano had erupted and this was the fall out.I also read that spores that cause hay fever are in the air,were you near a field ?..all speculation im afraid.
Possibly also the secretion from insects which is why I suggested to try soapy water. The insects in my greenhouse cause havoc with the gunge they leave everywhere and at first sight that also appears to be slightly oily.
------------- 'A sure cure for sea-sickness is to sit under a tree'