Mystery simultaneous top and bottom LEDs flashing

(ancient MyBook Studio Edition II, silver, 2x Firewire, eSATA, USB)

I think my boot drive’s W/R actuators are broken but I’d like to confirm if this error light pattern indicates a hardware error – I can’t find it described anywhere!

This is not the alternating top/bottom “RAID degraded mode” pattern as described in the manual. It’s the top and the bottom in sync, about every 1-2 seconds (but I wouldn’t call it “fast” as the “Over-temperature condition” is described, and besides it’s NOT hot).

Thanks in advance for your help!