OK, So I have intermix in my coolant, the brown coffee sludge in the recovery tank and have started diagnostics.
My mechanic says step one, he is going to test the coolant for exhaust gases using a "combustion leak detector" product. I looked for other threads using this stuff and saw nothing. Basically, you heat the car up and draw air from the recovery tank. If the test fluid changes color, there is exhaust gases present in coolant. Normally, this would diagnose a blown head gasket, but I am pretty sure this isn't the issue.
next I want a compression test and leak-down.
Is there anything else besides a oil cooler failure (heard this is rare), o-ring failure (again, rare) that causes intermix besides the dreaded cracked head? I haven't heard too many happy stories with intermix, so...
150K on a 2000 Boxster S