Silicone overspray on windows

Hey Guys
We had a window cleaning job today in Naples, the worst silicone overspray we have ever seen.
Usually we can remove the silicone with steel wool 0000 but it was not shifting this, it has basically been sprayed all over the windows, the residents had a leak (caused by whoever seals the windows didn't) so they waited until this was fixed to have their windows cleaned.
What does everybody use to remove this, we used a green chemical, a plastic scraper (don't use a metal scraper as too many cheap painters in Naples who use these and ruin the windows, we cover ourselves by not using them)
Do you use a paint thinner? also I guess there is more time involved in this so we need to charge more.
Can anybody advise.
Which cleaner do you buy and does it really work? We also have a major problem with hard water stains here in Naples, have you tried the Winsol Crystal Clear 550 for this?

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