The mercury optimax oil is supposed to have some proprietary additives that are good for their engines hence the significant sticker price. The dealers also like to hint that there will be warrenty issues if you don't use the Optimax oil.
I choose to beleive that all engines are built with the same steel and that oils that pass the requisite testing for the specific viscosities are going to get the job done. I have been using the Walmart 2 stroke oil for the last five years(it's A LOT less expensive and I use cases of the stuff). Our current 2-stoke outboard is going into it's 3rd year and just topped 1,000 hours with no problems. I sold the previous carburated outboard due to cold-starting problems in the winter not due to oil-related wear issues - the fuel injected 2 solved the cold start issues. If you can show you have been using a 2-stroke engine oil meeting the owners manual specs you are not going to loose a court case on warranty work. Whichever 2 stroke oil you use it's a good idea to keep using the same brand consistently.
I waiting for a flaming from the brand loyal guys.... I'm not saying that the additives are not a good thing, just saying that I don't beleive they justify the price delta and that you can run your outboard for a very LONG time without them. We run our our boats more in a year than lot's of folks do in the lifetime of their outboard...
