When the Roatax engines sit for a long time the rotary valve seals will leak oil into the engine.. The only fix is a complete rebuild.. That being said clean the engine out like you did, then run it for a while. Carry a spare set of plugs because you will most likely foul the first set.. I have found running them really helps.. You may get a little extra smoke when you first start it and keep an eye on the oil level in the tank.. My experience is that once you get it running you will be ok.. I bought an old ski tha had the came issue, once I ran it for a while it's great..