Try some paint thinner the type you use to clean brushes coated with oil base paint. If the material is gooey try removing some with a small plastic scraper.
What was the original position of the wheel before you moved it? This will indicate the location or direction it came from. Most bearing greases will flow at around 250-300 degrees F and usually are not translucent. My guess is the material came from something overhead. Was the car covered with some type of plastic material that was tied down with plastic ties? The temperature in the un-AC'd building probably got very high and melted whatever. Just some guesses.