First thing is to clean the oil up and run the engine with the bike stationary so that you don't have wind blowing the oil away from the source. One rule of thumb is, oil like excrement doesn't normally run uphill. If it's inside the belt housing you have the two seals already mentioned, the two cam shaft seals and the crank seal. Normally these aren't either expensive or difficult to change. If it's outside the timing case then look first at the rocker covers and the cone shaped seals around the rocker cover bolts. BTW - Be careful tightening the rocker cover bolts, they break off easily with over torqueing. One thing I do when installing new rocker cover gaskets is to glue the seals into the cover with a thin line of super glue. It makes it much easier to install the seals without having them twist or pop out of position as you snug them.