Wouldn't soap dry the vinyl? I have the same issue and used simple green which normally works for most of my cleaning needs. Sometimes a samll bit of Castrol Super Clean works well too but it's very drying. Don't know that I'd use it on vinyl.
Not meaning to hijack here but I'm kinda looking for the same answer. The other option I am exploring is the interior paint. Not sure i want to do that just yet. Trying to find a better solution...