I haven't really looked for 'friction points' on the convertible top, and don't think I will right at the moment (It's dark out!). But my guess is that something like this...
...might be a good choice. People use it, for example, on bicycle chains (instead of oil or even things like WD40, which can be a little messy and hold dirt). This stuff lubricates with a wax, stays dry.
It does come out wet initially, so I'd take steps to avoid getting it on the fabric of the top itself.