Hiya Vince..

I would tend to agree with the others in that it's probably the packaging oil and should have no effect on performance. I have bought...well...more than one new YS engine over the years and left them to "mature" on my shelves. When they are new they are actually sorta sloppy with packaging oil, so much that the bag will even be saturated with oil, it's sorta thick and sticky stuff. I have noticed that what ever type of oil it is will evaporate (?) or basically go away after sitting for some time.

I suppose they expect you to use the engine just because you buy it??? Well I like to plan ahead (apparently 20 years ahead)....

I'd venture to say the reason you see the staining on the upper surface and not the underside will be because the fluid puddled and remained thicker on the top and evaporated (?) quicker on the bottom. Just a guess...

I would not let the staining bother me in the least. It may even clean off with a little elbow grease...

Good Luck and Have Fun...

Chuck