I used a pair of long needle nose pliers. Make sure the diverter is clear of the threads by
loosening it with a 3/8" allen wrench.
The technique for the pliers is reversed, though, as I put the nose ends into the diverter,
and then pushed outward on the ends of the pliers handles. That makes the needle
nose ends grip the inside of the nylon center circle. Then try to lift it upwards. This will
probably take several attempts, but it should loosen and eventually lift upwards and out.
Plumbers have special tools to do this real quick, but I don't know what they are.
I think the diverter lasted about 12 years, so that is good. The new diverter works like new.
Happy Camping!