FWIW, After trying ball links, clevises and Z bends, I settled on using a 90 degree bend with the end going down thru the servo arm, secured with a "half clevis" type of retainer... simple, few parts to fail, reasonably cheap and nearly bulletproof.... Usually need to drill out the servo arm holes, so can pick the right size drill to ensure no slop... If a lot of adjustment is required, will use a screw type clevis....

Cheers!

Jim