DIAGNOSIS The keyless chuck's internal jaws or bearing race are worn or contaminated. This is common if the chuck is dropped or used with impact force.
FIX This is a chuck assembly replacement. Part number is 2 607 001 017. You need a 10mm Allen key. Remove the screw inside the chuck (left-hand thread). Use the Allen key in the chuck jaws to unscrew the chuck from the spindle (right-hand thread). Install the new chuck and reverse the process.
IF THAT DIDN'T WORK If wobble persists with a new chuck, the spindle itself is bent. This requires a full gear housing replacement. The tool is likely damaged from a severe drop.
HEADS UP Always secure the bit fully. Insert it, hold the chuck collar, and tighten until you hear three distinct clicks from the ratcheting mechanism.