I found an alternative to washers for making gear bits run reliably - use a cog or a ball to add weight to the top!
This also makes a single gear bit behave reliably like a simple blue bit.
Using two weighted gear bits one can also capture balls and trigger their release using another ball.
I have made a short video to demonstrate:
One thing I forgot to show is that if you attach the weight on the side instead of the top then it always returns to that side - it behaves like a green ramp.
In theory one could make a version of turning Tumble where the whole board is non-removable gear bits, plus adjustable weights and cogs.