I did have a question about the GPS module though. Both of my SecureSync units have Trimble GPS modules. I purchased a generic u-Blox M8T module to try to upgrade one of them to support Galileo and BeiDou, but the system does not recognize it. I am unsure if it is either incompatible or defective. The form factor of the module is identical and it bolts straight in, so I figured it was a standard. If you still happen to still have your unit, can you tell me how you checked your M8T module?
I actually have the same problem with two of my SecureSync 1200 units. They're old (serials in the 2000s) and did come with the Trimble Resolution T GPS cards. I have yet to get them to recognize the uBlox M8T module I had laying around, _however_, my newer SecureSync 1200 units (serials in the 22000s) talk to the uBlox M8Ts just fine. There are hardware revisions between the 2000 serial units (Rev B) and the 22000 serial units (Rev D), but I haven't seen anything obvious outside of some deleted caps around the onboard switchers. Depending on how spicy I'm feeling this weekend, I may break out the microscope and have a close look at the circuitry around the oscillator/gps section of the board to see if I can find differences.
I'm still investigating, however my guess is the firmware on the timing processor (back of the board in the same location where the SBC sits on the top) differs between the two revs, which would explain the skew around which units can talk to the newer uBlox modules. There's no easy way that I've found to dump the firmware off the flash chip (it's also BGA

), so that's a dead-end from my perspective.
If you're feeling exploratory, it may be worth poking around in the Linux image as well, there are a ton of binaries in `/usr/bin` which seem to correspond with API calls to the timing hardware.
Sorry I don't have a solution for you, but I figured I add some data and let you know you're not alone

.
PS: One other thing to call out is that my older units are using OCXOs, whereas my newer units are only TCXO. Which oscillator does yours have installed?
Edit: The firmware I'm running between the old/new units is also the same (latest from Safran 6.1.0)