Thank you so much for that input… Your suggestion was 100% spot on.
I will go on to say that I made the change you pointed out and the problem actually got worse. Before the change, the router was trying to send the traffic out WAN2 but it then failed back to WAN1, even though the route said it was reachable. After the change, the route was sending the marked packets to the IP in WAN2 as it should but there was no connectivity to the outside ISP links.
The final solution there was that on my mangle rule, I was specifying “Local” as the In-Interface which needed to be “Bridge1”, since there was a bridge, and Ether3 (renamed “Local”) was a member. I cannot count how many times the bridge interface has kicked my tail in this fashion. I only include the info here to help someone else out who, like me, forgets the bridge interface should be referenced instead of a physical interface if it a member of a bridge.
After fixing the mangle rule in-interface issue, I went back and reversed the Route Gateway back to WAN2 to verify and as expected, I was back to where I was before I started. I applied your suggestion again and everything is now working exactly how I wanted…
Anyway, thank you again for your quick and concise answer to my question…