I had that happen to me when replacing my spindle on my W210 recently.

I ended up using the floor jack to force the joint together, to create enough friction between the arm and the stem, so that when you snug up the nut the stem does not spin.

Can't understand why they don't put an Allen key hole on these stems, it would make it sooo much easier....

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech