Different from the drawing of Magic Static, your setup might also be with the motor 'in the middle' between the limit switches, instead of at one of the ends.
This other setup I found pictured on this site: xxx.redrok.com/led3xassm.htm (hope this 'link' is allowed?)
(see subtitle "how limit switches operate").
After changing the wires on your east limit switch, you could check the diode function in this way:
While the motor is moving towards the east limit, manually switch the east limit switch, briefly is long enough.
If the actuator stops instantly, the diode is still OK.
If the actuator continues moving, then the diode is shorted and must be replaced; or still something else is wrong (that is the reason why I suggest only brief testing this way!).
BTW you could also first measure the one-way conductiveness of the diode with a multimeter, while it is not connected to the switch.
That usually gives the same result as testing a diode under operational conditions.