JohnM. was right (2nd post above). I finally had to pick up the seal washers from the dealer. The two washers are 10mm, but the pan is copper and the torque converter is aluminum. I changed the fluid and filter this afternoon. The seal washers last installed by an independent were both aluminum and they obviously worked fine.

I noticed that it is pretty easy to line up the torque converter drain plug by lying underneath the car and using a 1-1/16" socket (close to 27mm) to slowly turn the engine over while feeling for the drain plug. The other descriptions I read made it sound difficult to do by yourself.