I used Dawn, full strength, on a soft brush the same day and VOILA! the greasy circles & bug body residue all came off nicely. Garage door looks great.
Thanks for all your valuable suggestions. I gained a lot of knowledge - Dawn is the go-to product for grease, laundry detergent is made to remove organic stuff, raising garage door makes the job easier, White Eraser is good product...gasoline...not so much.
Enjoy the day!