Its really tough to remove oxidation from the cooling fins, I have used fine steel wool in the past with success, but I usually just hose it down with WD40. Yes it will smoke for a little bit, but not bad and it burns off quickly,and there is a lingering odor of WD for awhile afterwards, but not caustic or annoying and it works great, especially on the black motors. Dawn dishwashing soap is an excellent all purpose cleaner degreaser, you may try a stronger degreaser for the front and bottom of the frame cradle and motor. If there is quire a bit, hose the whole motor down with it (while its cool) and use a high pressure sprayer. Then after you clean it, use the WD as a dressing. There are not too many over the counter products that will damage the finishes, stay away from bleach and acids. The finishes are pretty resilient and will stand up to strong degreasers, that will clean any old wax off, but thats kind of the point you want to take it back down and put your choice of wax/finish on the painted surfaces now.