Planning on using a 6 hp Tohatsu 4 stroke on an 18 foot Sotar raft on a VERY long Yukon River trip. New outboard broken in last summer and running great. Got the factory repair manual and am putting together a maintenance parts list to include spare water pump. I have little experience with a small outboards on the silty Yukon and am trying to decide if having adequate spare parts will suffice - or do I need to actually take a spare motor (or have one ready to ship to a village along the way as a replacement). I just have no idea how reliable a water cooled 4 stroke will be in this kind of silty water. I do plan on changing oil and drive shaft fluids during the trip and will have provisions for flushing the water pump system. The raft is outfitted with an excellent rowing set-up, but I believe the motor will be "required" to combat the constant up-river winds for the long trip so I consider the motor very important to complete the trip. Any advise/suggestions would be most appreciated. Thanks.