CLK500 staining driveway. Garage says nothing wrong. Help?

[shentodj]

My wife's 2003 CLK500 has, for the last few months, left stains on our driveway. The drive now has rust coloured patches (2ft x 3ft, so not small!) and also circles of white; the white being around the edge of some of the puddles and is left when puddle evaporates.
My wife took car to garage a month ago, they wiped all of the underside, couldn't see any leaks, checked water & oil levels (all OK).
Car still causing marks.
Wife just been back to garage tonight. All same checks,all OK. No levels down.
The only thing I can think of, where a car leaks without it showing on levels is air con condenser drips. Anyone know where it is and could it cause the problems as described?
Anyone got any other suggestions to check?
Thanks in advance for your help,
Shentodj

[anonymous-user]

Rust? It is a 2003 Merc after all

[PositronicRay]

A/C shouldn't leave such large puddles, unless you leave it idling A/C on full blast for hours on end.

Try catching some in a tray or on a sheet of cardboard then the sniff & taste test.

Difficult one as all the levels are ok, I wonder if it's screen washer fluid?