I'd say your assumption is correct. I'd replace them with the Oldham style couplers. My X2 conversion for CNC fusion used Lovejoy coupling with rubber spiders. I had around .005" backlash as well. Luckily Lovejoy has the .dxf files of their spiders online so I downloaded them and CNC'd out spiders made of an old cutting board. My backlash went down to .002".
The Oldhams are easy to make. The insert is cheap enough it's probably not worth making that part however.