Matt
If you suspect that it is condensation, then remove the rocker cover and wipe out the offending mayo. Replace and go for a long drive, an hour or so, keeping a very good eye on the temp gauge. A long run should allow the engine to heat up enough to remove any moisture from the oil. Remove the oil filler cap, check the inside of the rocker cover when you return. No mayo then condensation, mayo then look further.
Hope this helps
Nick