by the way if your Raggtopp layer is getting thin you can tell by how long during a downpour does the beading effect last. We had some heavy rain here in New Jersey recently, I mean like monsoon waterfall heavy and the beading quit after about 30 minutes.
Haartz also warn against using any detergents or soaps on your top. Apparently they attract dust which is what you want to avoid getting in the fabric at all costs.
A stiff stream of water during the hot and dry summer months is a great weekly practice. (Renovo for the the plastic window is doing wonders for me)
Here's the brush from OXO (feathertip) I use to clean the top when bird droppings pay their unwelcomed visit. That stuff is toxic rinising off may not get it all off.
I also use this type of brush around the bottom of the car and under the rear and front bumpers, wheels wells etc. It lifts dirt without stripping my wax.
http://www.autopia-carcare.com/wps-2148.html