I have never bothered with the stock arm.
My SL-1210 has a custom off deck traffo and DIY PSU and Foculpod feet other than that it is standard.
First I tried an all O.L modded Rega RB250. Detailed but rather flat sounding.

I then tried an Parallel tracking Terminator air arm - huge improvement over the Rega but stil what I will describe as 2D and a big lumpen.

I then got a PL-71 and that blew the 1210 away on boogie factor and what I will describe as musicality - 3D and the opposite of lumpen (whatever that is?).
The SL-1210 sat in the corner for a while.
Having tried different mats on the PL-71 and finding they change the way the notes tripped of the thing I tried the SL-1210 with the favoured PL-71 mat. Pretty good - This was with the air arm.
I then made an arm board for the Technics to take the PL-71 arm.
The result is really rather good.
All the pitch stability of the Techi but with the boogie factor of the PL-71.

All of the above was with the same 33PTG cart and phono stage.
Now I can switch arms easily and will live with both decks for the foreseeable future.
Some have said a modded 1210 really needs a good arm. Preferably SME or Jelco. Some rate the PL-71 very highly. I think the arm is a good one.
I think the modified SL-1210 is a good deck and deserves a good arm.
Those who think it sounds like a CD player - have you put the right arms, mats and carts on it?