How to change door mirror glass on 1998 R129

Only maybe. I just did thi son a 126 and if the mechanism is similar this should work.

Push the mirror back so it's parallel with the body. If it's a bit reluctant to move, spring some WD40 or silicone spray in there.

Now if you look at the tip about 2-3 inches inside you'll seee two spring wire ends on a plastic hook. Using a flat blade screwdriver disloge them off the hook. Now the mirror can by levered out from the front.

To put the new glass back in, put the spring on the new glass securing the hooks over the catch. Put the end that catches on the moving mechanism in so it catches then pess back until you hear the reassuring "snick-twang" of the spring catching.