Hey,
I've actually heard good things about Autoglym too, though I haven't personally used it. For a general fabric cleaner for interior, I've been using Superclean Diamant, which I order from Mister Auto (
http://www.mister-auto.co.uk/en/), and I like it. But I have absolutely no idea if it will work on the convertible top fabric. You would have to check what's in it.
First, is it fabric or vinyl? This makes a big difference between cleaning products.
A friend of mine has a fabric top and actually uses Ragg Topp cleaner and protector and swears by it. I don't think this will work on vinyl though.