We are using PureSight, but I don't think that is the problem
Well, it might be better to ‘know’ than ‘think’; have you considered either disabling PureSight for the sake of testing, or create a new WWW Proxy on a different port without PureSight attached to it, and try to update Yum through that?
I understand that:
I don't want to do 2, 3, or 4. I want to do 1 above
But for the sake of trying to help, have you considered trying a TCP Mapping?
For example, right click an existing proxy in WinGate and create a new TCP Mapping.
Select a unique port number e.g. 88, that this service will listen on.
For the mapping address enter in the address and port number for this repository.
Then enter Yum's setup and configure it so to do a direct connection to WinGate servers IP Address on Port 88, then the TCP Mapping will just relay it to the repository.