Not familiar with this particular model but test riding should not be a problem provided the leak is not too serious. The engine oil in a 2 stroke only lubricates the gearbox and clutch. Lubrication for piston and crankshaft comes from 2 stroke oil so they won't be affected. Some oil seals are fitted from outside, in which case, you can pick out the old seal and drive in the new seal.If seals are fitted from inside, usually against a lip, then you would have to split the engine.Carefully examine the aperture where the seal is fitted. If it is parallel,then pick out seal and replace.If the opening in the casing has a lip on the outside of seal you have to split it. If you can identify the number on the seal, you may be able to get it from a bearing and seal company, cheaper than main agent.With a new seal in your hand, you will be able to tell if it can be fitted from outside. Depends how bad the leak is. A small leak is not a bad thing as it means you are regularly checking and correcting the oil keeping it refreshed. Parking the bike leaning to the right will help to reduce the amount of oil lost.