Hi there,
Yes, I did resolve this in the end. The key for me was Static Routes on the Wireguard Gateway VM on my local network, I also set a static route on the Endpoint to send any traffic with my LAN IP addresses back over the wg interface.
I didn't realise that if you set your wgx.conf to use AllowedIPs= 0.0.0.0/0 it forces ALL traffic over the wireguard interface, so returning traffic never gets back to the client that initiates the connection.
Anyway, a picture is worth a thousand words, and see my updated diagram here. Apologies to the Network Engineers out there. I'm not a pro, so I guess my diagram is pretty amateur! It serves it's purpose for me as documentation though :)
In the pic, you can see the routing table on the WG Gateway VM and the WG endpoint. The routes in Green are the ones I added manually, and it all works like a charm now. Also, note the MTU thing, that caused me no end of grief, so if you have issues with SSL handshakes failing and other random stuff....check your MTU.
WireguardPublic3.jpg