oil in 968 coolant

I was at laguna seca and had some quarter sized oil drops in my coolant expansion tank after my first 20 min session, (2 misshifts) and a redline..I was concerned and kept an eye on it and the coolant level, when I got home 49 laps plus 100 freeway miles later there was no visual signs of oil in the coolant and neither the next day... Do I have a weak or failing cylinder head gasket or could this really have something to do with an oil cooler????    1994 968  - VIN#   WPOAA2967RS820761