The Marvel Mystery Oil or Kroil should help.

Now a story (true). I worked at a boat yard once. One of the customers 440 powered boats sank in salt water... something silly like a sea cock opened. The boat was raised after a day or so and a day or so later the 440 was pulled, drained and immediately dropped in the outboard test tank. The test tank had fresh water a bit oily from testing 2 stroke outboards. It sat there for about a month. When the mechanic was ready to work on it, he pulled it out, drained it again, put some oil in the cylinders and got a long breaker bar. It was stuck. The breaker bar got it turning. With electrical parts replaced, it was re-installed and fired up. Ran fine. Far as I know, no problems afterwards.