I did a search for the thread with more info on the Zep product you mentioned, but I couldn't find it.
The only Zep window cleaner offered at the Home Depot in my area is the one below.
ZEP - Zep Glass/Tinted Window Cleaner Concentrate 3.78L - CA1052128 - Home Depot Canada
I am not sure if its the same stuff or not.
I took my truck and snowmobile trailer to the local truck wash bay, trying to do something good like cleaning the truck turned into a nightmare. I guess the guy ahead of me was washing his semi truck, and he got grease or something nasty all over the hose, then the hose rubbed against various parts of me during the course of washing everything, and I hopped into the truck and got it EVERYWHERE. My wife tried her best with a cleaning product we picked up locally, but I think it only made things worse. It did manage to get the grease off, but now there are massive spots where the cleaner was sprayed that look terrible.