From what I've seen with various plastics, the plastic it self is deteriorating / out gassing not any sort of coating that was applied.

With regular use the failing layer rubs off / gets covered in dirt , let the car sit and it just gets sticky.

I've had US domestic cars steering wheels look like someone had covered them in rubber cement after a few months of non use.

I'd probably try denatured alcohol to clean or some similar colored "dirt" powder to cover the stickyness.

Modern plastics have a ID stamping so if you could find what type of plastic is being affected some research could be done.