Oil Leak after long journey (RTTS)

Hi Guys

Just returned from rtts, on the way back when we stopped in a service station I noticed oil coming out of the breather pipe, the air box was covered in oil, the engine runs fine with no problems, I topped the oil up and carried on.

Does anyone know what this fault can be?

Only happens after driving constantly for 2-3hrs.

Rtts 2010 - Legendry