I applied the steering motor upgrade to Monster Herbie this morning, as well as making a couple of other tweaks.
Steering is much more positive, and I even managed to get the hole on the PCB cover right!
I replaced the green motor gear with a black ZZ one because the green one looked and ran a bit ratty.
I also upgraded to the red motor for a little more torque. The speed increase is eaten up a bit by the lower gearing so I'm still very pleased with the results.
Of course the stock tires are way better for crawling!