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My experience with VW/Audi stuff:
- The coolant does look dark to me. The Pentosin VW coolant I use stays very pink.
- The reason for the special coolant is that all the other coolants seem to eat head gaskets.
- I'd take that sample you have and just let it sit in the corner of the garage undisturbed for a week; see if there is anything floating on top after a while.
- There is usually an air purge screw somewhere in the cooling system at the high point. That said, I often find it necessary to drive a car up/down steep hills while at temp and the heater going full blast to purge all the air out of the cooling system.
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