I rewrote your code and changed the pin names to motor1 and motor2 to make it easier to understand.
I also added comments and made changes to bring the motors to a stop for 2 seconds.
Read the code over carefully and tell us if this is what you want to do.
Also why do you think your Uno was faulty?
const int motor1 = 9; // connected to the base of the transistor
const int motor2 = 10;
void setup() {
// set the transistor pin as output:
pinMode(motor1, OUTPUT);
pinMode(motor2, OUTPUT);
}
void loop()
{
digitalWrite(motor1, HIGH); //turn on motor1
digitalWrite(motor2, HIGH); //turn on motor2
delay(10000);
// motor1 is still running because we have not changed digitalWrite for motor1.
digitalWrite(motor2, LOW); //turn off motor2
delay(2000);
// now turn off motor1 and both motors will be stopped
digitalWrite(motor1, LOW); //turn off motor1
delay(2000); // tank will be stopped for 2 seconds
}