@keen360, I'm following up your PM.
This is your bridge PCB:
https://i.imgur.com/AP2YzPu.jpeg (component side)
https://i.imgur.com/vRazZY8.jpeg (bottom side)
These are your two eBay candidates:
https://i.ebayimg.com/images/g/qLoAAOSwAG5j2vI8/s-l1600.jpg (PCB #1)
https://i.ebayimg.com/images/g/PTMAAOSwnHNj3YZR/s-l1600.jpg (PCB #2)
All three PCBs appear to have an Initio INIC-1607E USB-SATA bridge IC (E = encryption). I expect that all support hardware encryption, although I have no idea whether this is always enabled.
There appear to be two PCB manufacturers used by WD, either APEX or ELEC (?). The YYWW or WWYY date codes (WW = week, YY = year) are 3609 (week 36 of 2009), 1011 (week 11 of 2010) and 0940 (week 40 of 2009). APEX uses YYWW, ELEC uses WWYY.
There are two main physical differences between the two PCBs.
Your PCB has a 5V regulator consisting of U7, Q5 and L5. One eBay PCB is similar, but the other has a much beefier looking 5V regulator consisting of L4, Q1, and NX7101IDM (IC).
The other difference is that the newer eBay PCB has a dual MOSFET chip at U5 whereas the other two PCBs leave this location unpopulated. Instead, those PCBs without this chip bypass it with two resistors, R46 and R47, each measuring 0 ohms (?). The MOSFET chip switches the +5V and +12V power to the HDD's SATA power connector. Basically, the difference is that in your case the HDD is always powered while the newer PCB enables the bridge firmware to switch off the power in standby mode.
On the back of the PCB, near the SATA connector, are two test points, TP5 and TP6. I suspect these may be the +5V and +12V SATA power supplies. Try to measure these voltages with respect to ground. You can use a screw hole as your ground reference. If both voltages are missing, measure the voltage on either side of L6 near the DC barrel connector. There should be +12V.
One more thing. There is a SOFT POWER pushbutton, SW2. Examine the markings on the enclosure to confirm that this is a standby power button and not a reset button. If it is a reset button,
don't touch it. Otherwise, if it is a power button, then see what happens.
In short, I expect that all PCBs are most probably compatible.