You won't be seeing any refrigerant on your window, as it will instantly boil off.

You're probably just losing some from the connection and spraying it around. A "manual" coupler helps a lot there.

What I see on the winshield is a few spurts of what looks like sap from trees but only happens when I work on the AC. Maybe you are right.

When I remove my plastic cap a tiny bit of freon/oil seems pressurized and comes out. Does that mean the valve is bad?

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1993 Benz-190E-2.6 liter