From control panel, I deleted GSX from all three of my simulators, leaving Addon Manage and Couatl. Launched each simulator, and confirmed in addons pulldown that GSX menu was absent, but couatl and live update remained. In FSX and P3Dv4 SODE v1.5.3 menu also appeared since they had been previously successfully registered and they tested ok. In P3Dv3 - the problem child - SODE v1.53 menu was not present, as expected.
So then ran GSX full installer v2.0.0.2 in all three sims. It did the basic install, the MS VC++ install, and then as you described passed control to SODE platform manager 1.5.3. As expected the tabs showed FSX and P3Dv4 SODE already registered and active, and as I expected the v3 tab showed P3Dv3 SODE as not registered. So I pushed the register button, and the Platform Manager reported SODE as now registered and active in P3Dv3. So I expected it might now appear as a P3Dv3 addon. However after finishing the GSX install, I launched P3Dv3, and discovered that SODE had not appeared in the options\addons list, and the SODE menu was still missing in the pull down addons menu, though GSX had now reappeared alongside couatl and couatl live update. Testing FSX and P3Dv4 simulators, SODE remained in the addons menu and the GSX menus had appeared, as expected.
So it is clear that in P3Dv3, even though the SODE platform manager registers SODE and shows it as active (does it somehow test it ?) the SODE activation isn't being picked up by my P3Dv3. I recall reading somewhere that addon package installation works differently in P3Dv3 and v4; that v4 addon packages can be "dropped in" and are recognized automatically, whereas in v3, the third party installer must have some specific code to do it. Could this difference be somehow related to my SODE package installation problem ?
Chuck