I cant offer technical comments, but...
Im happy to share my bio, but i do make it very clear that its on the other persons head. Ive never sold a single drop, so anything from me has always been a freebie with no warranty given nor implied.
I guess what im saying is that youre talking about "rather not risk it..." and im saying you should make sure that, whatever happens, the car owner knows its their risk and *not* yours.
If they then choose not to use it, well, so be it - but at least you know it wont cause family tensions then! : )