Two Words, to both of you: Oven Cleaner.
Not on the aluminum stuff, just the metal parts.
Metal parts, get a five gallon bucket with a gallon of royal purple.
Add water, soak for two days.
Vinegar, 5 gallons in a bucket is cheap.
Paint thinner, get a bucket you can cover at night.
Buy the paint thinner at an automotive paint store, and throw five gallons in the gas tank for a week.
Thank me later, pm me for questions.
P.S. Synthetic, grease, brake fluid, trans fluid, ETC.