I purchased a heavy, sticky bottom, dished disk thingy (approx 6ins
dia) which enables me to hold a sat-nav on top of the dashboard and it's
worked superbly for the first 9 months or so, not moving at all during
heavy breaking or accelerating. However the stickiness of the base seems
to have degraded and I now have to catch it if I accelerate,
particularly up a hill.
The combination of a heavy canvas toroid filled with what maybe lead
shot, a sticky base and a smooth plastic surface to fix the suction cup
to was very successful for a time. However :-( .

I don't have the original instructions or name of the product.. I bought
it in a "motor mania type shop" some distance away.

Does anyone know if it's possible to treat it in some way to recover
the stickiness? perhaps wash it? or re-coat it with something? or do I
just bin it and look for another one?

Don