This 030 form-factor motor with precious-metal brushes offers pretty good performance for a flat-sided motor.
Offering 7400 rpm @ 4.7V, drawing 150mA and giving 4 gm*cm torque (17 @ stall).
Solarbotics finds it runs a bit longer per solarengine discharge than the old motor, and the 1.5mm output shaft is a perfect match for the RW 10mm diameter wheels.
A touch of glue, and you've got an excellent tilted wheel platform (like for Herbie robots)!
And if you need a friction fit, the included RW PRET (Plastic retainer) you get with the RW wheels press-fits on too.