i have a 1975 porsche that i am going to have painted. the oil tank is in the right rear wheel well. there is baked on oil all around the area. i have tried bio-friendly degreaser, but it only took off the light stuff. i also used wax and oil remover,but had to scrub like hell. what should i use? i don't want to harm the paint as i do not want to break the undercoat protection. any suggestions will be appreciated.