Vintage ARxb turntable. Refurb or replace

The AR, if it is in good working order is surprisingly good.  The arm looks rather agricultural, adjustments are rather clumsy and the only antiskating is provided by the twist of the tonearm leads, but it works well.  The headshell mating pins wear quickly so push it into the arm and then tighten the collar rather than using the collar to draw the headshell into the arm.
There is tons of information out there on how to restore, modify, or upgrade ARs, but it sounds like you might be satisfied with a simple refurbishment, which you might do yourself, though there are reputable people who focus on AR restoration.

Look at the suspension rebuild parts available at Vinyl Nirvana. I rebuilt the suspension  of my AR "the Turntable" (1984 mfg. date) three years ago. Not difficult or expensive and the results were amazing. You can also replace the motor if desired - but not necessary.

I would suggest you consider replacing the tonearm with a vintage SME or Jelco. No essential but better than the AR standard.

the arm is the problem on the table

it sooo affects the sound

You can always replace the arm If you want, but I must say properly set up that’s an excellent table.  Keep it.

I use my 46 year old 1229 everyday.  It’s my favorite component.
The AR is likewise excellent.

 N.

Since I just discovered this thread I’m late to the discussion, but I have a strong opinion on the matter.

The AR-Xa and AR-Xb turntables are phenomenal turntables and are well worth preserving or restoring. Spend a few bucks to “mod” the AR because you will have to spend a great deal more to get the same kind of sound from a replacement. I went down that path and wound up going back to my Xa, which still sounds better than the replacements. 
Get a replacement motor, a new belt, and check the pivot for signs of wear. Vinyl Nirvana is a good source for parts, and Vinylengine is a terrific resource for advice. The most radical mod that I had done was replacing the tubular arm with a similar S shaped arm from a Technics that accepts a universal cartridge shell. You can keep the original pivot assembly and don’t have to replace the entire arm. I only did that because I like to play around with swapping out cartridges and the original AR cart shell is notoriously difficult for that. If you always use the same cart, the stock AR arm and shell are more than adequate.

Oh, and don’t forget to spring for a new replacement dust cover. They don’t hit the tone arm and they look fabulous!