I think Dawn dish detergent might help. It really cuts grease well. I use it to clean my hands after working on cars and have used it to remove pine tar fom my hands after cutting pine trees. I admit though in both cases the stuff had been on for hours not years.
Try #7 auto Bug and Tar remover. It is available at most hardware stores in the auto section. Costs about $2.19 for 12oz can which should last you the rest of your life. Stuff smells just like kerosene, charcoal briquette lighter fluid, oil lamp oil etc. If you have some kicking around, try WD40. If nothing else works, there is a product called Goof Off that will probably remove the tar, the clearcoat and some of the paint. Might be best to test any of the above in an inconspicuous spot. Good Luck
Eucalyptus oil is good for organic stuff like tree sap or chewing gum. So is what we call Shellite or white spirit - a clear light petroleum-based fluid which I think you might know as Coleman fuel. There are some orange-oil based solvents around now which should get it off, but I'm not sure what they might do to the surface finish.
Dow scrubbing bubbles bathroom cleaner(don't laugh). It's cheap, and it won't damage paint. We use it on the tractors and our trucks. Also, if it's available to you, greased lightning works really well, but try it diluted first. It will eat paint. Also removes fuel oil, never seize, etc.
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