In the Rambo pins file, it says...

//
// Servos
//
#define SERVO0_PIN 22 // Motor header MX1
#define SERVO1_PIN 23 // Motor header MX2
#define SERVO2_PIN 24 // Motor header MX3
#define SERVO3_PIN 5 // PWM header pin 5

I think the 'smart' thing to do is find where pin 22 is on your board. If you can't find a picture that details it... You can turn on the pin debugging and use an LED to look for it at various locations. You would do a M43 T S22 E22 R999 W300 and look for a pin that makes the LED blink.