Mayonnaise - Panda 100HP

[Hoolio]

I'm looking for a cheap run-about and a Panda 100HP fits the bill nicely. Cheap to run, fun to drive and a bit different. I went to see one today, good spec, service history, cambelt done recently and a good price BUT when I took the oil filler cap off there was a little "mayonnaise" in the top of the cap. Having a looked at various forums this could be either an early sign of head gasket failure or it's condensation build up due to lots of short journeys.

Any way to check for sure which it is?

Thanks