I just replaced bearings on a Mag 91 four stroke. I had about 6 gallons of fuel through it over a two year period and three really hard crashes and the nose bearing was a little rough.

When I tore it down, there was no rust, just some baked on red from the fuel. The wrist pin pulled right out. No indication of any rust. I ran Omega 15% in it and never ran it dry at the end of the day, and never used any after run oil. I also never pumped the tank dry, but just pluged both lines. It was almost a year after it last crash before I finally tore it down, so if it was going to rust, it would have by then.

I think a lot of guys confuse the red baked oil for rust. It isn't. Rub your finger across it and if your finger turns up red, it may be rust. It it comes off clean, it baked on red dye from the fuel.

I use after run, but only on a rebuild, to make sure things have a bit of inital lube on their first run.

I think you can love an engine to death. They don't require a lot of fussing, just try to keep them clean and run good fuel and they will last a long time with no problems.