"Where exactly is the idler arm? (i'm still not quite familiar with the english terms)"
The idler arm is symetrically located to the Pitman arm, which connects the steering box to the steering linkage. Probably the bushings are due if original. I don't think worn sway-bar bushings will contribute to your tracking problem. Do a formal wear test of the ball joints, check all suspension attachments for looseness, and check the struts mounts.
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7