The site is exactly where Andy said. We've both physically been there and can assure 100% it is there. Unless something has changed in the last two weeks..
As I mentioned in the other thread, I was doing some monitoring in the past 2 weeks in the south Durham area, and briefly drove thru the north end as recently as the 26th. I don't think I would have picked up a signal from Uxbridge as strongly as I did at 401 x Brock Street, but stranger things have happened.
Could these sites be part of another Simulcast system?
That entirely could be possible.
The following sites share the same frequencies, according to TAFL (which I know isn't perfect, and doesn't always have 100% accurate data, but is the best source available):
The TAFL search used was "Metrolinx o/a GO Transit" - 3 licenses are listed in TAFL, 2 of which are 400Mhz ones (the other is microwave).
These sites have all the frequencies that have been identified in the RRDB as being in the "001-001" simulcast sites, as well as 412.2875.
CIU608 - Aurora, ON - 240 Orchard Hts Blvd
CIU321 - Innisfil, ON - 112A Valleyview Dr
CIU322 - Mitchell's Cnrs, ON - 5209 Enfield
CIU609 - Toronto, ON - 301 Front St (CN Twr)
The following two sites both have the same identical frequencies, with the exception of Waterdown having 1 extra freq 413.9375:
CIU662 - Waterdown, ON - Mountain Brow Rd
CIU661 - Hillsburgh, ON - 5200 Wellington 24
The following two sites share the same frequencies, with the exception of Pickering having 1 extra freq 410.9125:
CFV291 - Pickering, ON - 3189 Brock Rd
CHP350 - Niagara Falls, ON - 5815 Morrison St
There is another Pickering site (different IC callsign and frequencies, same location), with some (but not all) of the frequencies used on the "001-001" sites, plus some other frequencies from various other sites including the "miscellaneous" ones mentioned below:
CIU660 - Pickering, ON - 3189 Brock Rd
It has no other sites with similar configuration.
There are a handful of other miscellaneous single-frequency licenses for Burlington, Cambridge, Georgetown, and Oakville, all using one single frequency from a known/confirmed site.
There are a ton of reversed-pair fixed sites (I interpret these as base stations etc) in places like Etobicoke (125 Judson), Mississauga (3500 Wolfedale Rd), and Newmarket (18110 Yonge St), etc. I have excluded these from my search.
There is no license for any site in Uxbridge on the 400MHz licenses, but there IS one in the 10GHz licenses. It links the Oshawa MW site with the Ballantrae MW site. The Ballantrae site has no other links to it, and the Oshawa site links to Churchill, Toronto, and Aurora. All this is strictly 10GHz, 0.141W stuff according to the licenses.
