Re: Marvel Mystery Oil, and it's best uses?
MMO has had a place in my shop for years. It's an excellent penetrating oil but slow acting. I've typically used it as a fuel additive to top lubricate engines. With the new fuels it seems to work well to prevent valve seats from being pounded down due to the lack of lead in the fuel.
MMO air tool oil is the only lubricant I'll use in my air tools. Been using it ever since I found out it was available. Prior to that I used the standard MMO. The air tool oil has a few properties that help dispel moisture from the tool.
I've also used MMO as an oil additive but have pretty much quit doing this as the newer oils are so good it's generally not needed. The old paraffin and non-detergent oils really needed the boost that MMO offered.
Your engine, having sat so long, may show clean oil but I'd change it anyway. As was posted it may have water laying in the bottom of the sump and/or the dirt and crud may have settled out while the engine was not being used. Really depends on the quality of the oil that is in the engine.
You mention the engine has good compression. I would think this would indicate the rings are not stuck. I'd still pour a couple tablespoons of MMO in the cylinder and spin the crank several times. A little extra lubrication on startup sure won't hurt it any.
If you decide to use MMO over a long period of time be aware it's available in gallon, five gallon and 50 gallon sizes. Cost per gallon goes way down over the little consumer cans most parts stores sell.
Aside from being an excellent lubricant and additive it, to me at least, has a really nice aroma.
A gun and a parachute are much the same. When you need one nothing else will really suffice.