Although I too suspect head gasket, could it be a leaking heater core? Smell of coolant, wet carpet, foggy windshield?

Also, I think your picture is showing a leaking valve cover gasket and/or timing cover seal. That timing cover seal is a common leak.

I just did my headgasket on my m103 and didn't have the valve guides replaced. The machinist who did the head for me said they were solid. The valve stem seals were a must though.

Other parts to consider:
cap & rotor
plugs & wires
head bolts
bypass hose (short hose between thermostat and head)
coolant

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1991 190e 2.6 190,000mi