You are amazing! Thank you!
I followed your instructions to the Lionel Parts List and searched "Product Part Number or Name" for the AD20 as I have been doing all along - Nothing! Exactly the same result that I was getting every time I ended up on that page in my searches!
I knew I must have missed something as you plainly showed me that you could find them. I went back and clicked "Replacement Part Number or Name" BINGO!!! Lionel Part Number AD20 superseded 691PCB1012 available and in stock!! Wow! I didn't think I could be that stupid! One is on it's way to me now!!!
Another question. If you don't mind, the MTH Proto Sound 1 Forward/Reverse Board has the coupler wire's connected in series, on the Lionel TMCC Board each EHR-2 coupler has two pins for the front and rear coupler. Do I remove the series cross over wire and connect both wires independently to the corresponding connector on the TMCC Board?