On Fri, 10 Aug 2018 10:52:41 +0200, Sepp Ruf
wrote:

the only rbt-relevant sunscreen quality is ... if it can be used as an
emergency chain lube.

Yes. Not perhaps a *good* chain lube but nonetheless. It's got oily
type stuff in it. Jobst Brandt's ride reports include mention of the
use of sunscreen as an emergency grease for a dry hub bearing on his
son's bike, on one of his trips to the Alps.