oil in coolant but not in engine... thoughts?

[evifenocvt]

so i picked up a boxster for a parts car a few weeks ago. the PO said that the engine blew a head gasket so sold it for cheap. the engine still ran but rough at best from what i recall. got the car home and began tearing down. first there were signs of oil in the cooling system. chocolate foam residue all over the reservoir and all throughout the cooling system hoses and radiator. but surprisingly no coolant to be found when i drained the pan. there was a bit of oil pooling around the top of the engine, left side only, so i suspect it might be some sort of leak/ failure from the oil cooler/ heat exchanger. right side of the engine is relatively oil free. from those observations alone, what preliminary rough conclusions can be drawn? no leakdown or compression check has been done. but i am thinking perhaps not a head gasket failure? thoughts, opinions... thanks.