No, I didn't check for play. I'm pretty much a newbie with car repairs so I'm learning at each step with the help of the fine folks here. Which part to I need to pull on to check the play?

I used to have a wagon and have all the paper manuals from MB and Haynes too..
One thing I remember is some serious warnings about pressure being in some places..
so I really suggest you find those FSM instructions about diagnosing this system AND STILL WEAR GOGGLES when working under there....
For the simplest and possible direction to look.... that arm at the back with the vertical link going from it... take that off... and feel to see if that arm can be moved by hand a little... you might have everything else ok and that position sensor not be working... I am being optimistic .... but others have described fixing even the large items at the back end as less work than I imagined by reading the FSM..