Yep, you are correct. It is TPO, I assumed because my first TT in 1997 was EPDM that this one was too. I know, usually excess Dicor is not a problem, until you need to take it off!
And then while trying to clean up the edges of the opening, I noted an unusual "bump" in the TPO. A little investigation found this:
Yep, gotta love "attention to detail!"