On my Bonneville, I appear to have something splashed on by back trunk plastic lems cover that includes the tailights. It does not come off easily - is there a special cleaner for plastic that can safely remove whatever this might be. It is strange - it is only on the plastic and not on the paint so whatever it is, it is firmly sticking to the plastic?

Try the Maguiers Plastic-X product. It works great for polishing scratched or hazy plastic, it should clean up the gunk?

Another product maybe badge and sticker removal spray, it works well on removing adhesives and might make for quick cleanup?

very good product

Any fine cut cleaner will help too. Plastic X is a plastic polish, there are many like it