I've tried again this morning. Same result.
The OS3 flashes green and red for several minutes as expected, and then the copy fails as below
% cp srf-osb-1.0-0068.bin /Volumes/BOOTLOADER
cp: /Volumes/BOOTLOADER/srf-osb-1.0-0068.bin: fchmod failed: Device not configured
This time, however, there is not a DEPACK.ERR file in the bootloader mount:
ls -l /Volumes/BOOTLOADER
total 0
-rwx------ 1 don staff 0 Dec 4 1983 SRF-OSB.RDY
The unit looks like it has both yellow and green LEDs illuminated, solid. Every few dozen seconds, it blinks rapidly for a few seconds.