FAN broken in RB1100AHx2?

I’ve a question about the fan in a RB1100AHx2.

Normally the output looks like this:

/system health print
           fan-mode: auto
            use-fan: main
         active-fan: main
            voltage: 12.3V
            current: 757mA
          fan-speed: 1952RPM
        temperature: 25C
    cpu-temperature: 35C
  power-consumption: 9.3W

But I’ve one Router which look like this:

/system health print
           fan-mode: auto
            use-fan: main
         active-fan: auxiliary
            voltage: 11.9V
            current: 1008mA
          fan-speed: 1156RPM
        temperature: 33C
    cpu-temperature: 37C
   ower-consumption: 11.9W

and one router which looks like this:

/system health print
           fan-mode: auto
            use-fan: main
         active-fan: none
            voltage: 11.8V
            current: 940mA
          fan-speed: 0RPM
        temperature: 31C
    cpu-temperature: 45C
  power-consumption: 11W

But the systems are stable, e.g.

/system resource print 
             uptime: 36w1d17h18m56s
            version: 5.20
        free-memory: 1514720KiB
       total-memory: 1555212KiB
                cpu: e500v2
          cpu-count: 2
      cpu-frequency: 1066MHz
           cpu-load: 2%
     free-hdd-space: 24388KiB
    total-hdd-space: 41768KiB
  architecture-name: powerpc
         board-name: RB1100AHx2
           platform: MikroTik

Are the fans broken or just not needed? do I need do make a RMA?

ps: we did not get a SNMP Trap that the FAN is broken, should we have gotten one?