The headlight of the RS 125 until 2006 consists of low beam as a lens headlight and high beam as a mirror headlight in a common housing with a headlight glass.
There can be many reasons to open the headlight, be it modifications such as Angel- or Devil-Eyes, the need for a restoration of the reflectors or even just for cleaning the headlight.
It should be noted in advance that opening the headlight was never intended. The headlight glass is glued to the plastic housing with black silicone.
First, the bulb and cable are removed, then you start to cut with a cutter knife as far as you can once around the gap.
The headlight is not glued evenly, the point now is to find a spot where the gap between the headlight housing and the headlight glass is as large as possible. Here, you will now need to try to cut through as much silicone as possible while driving a screwdriver or other object between the glass and the housing. While doing this, continuously try to cut through other silicone in the vicinity.
Under no circumstances should you try to pry out the glass with the screwdriver, as this will damage the glass.
The purpose of this exercise is to keep tension between the plastic housing and the headlight glass in order to keep widening the gap by constantly cutting the silicone and cutting more silicone. The further you get with cutting, the more you can try to drive the screwdriver between the glass and the plastic housing.
Once you have cut larger areas free, you can now drive the screwdriver longitudinally along the silicone seam to the sides. If you were to bend the headlight open further instead, the tabs on the sides of the plastic housing would break off.
Once the glass is removed, the high and low beams can be removed from the housing. All screws on the back of the plastic housing are exclusively for turning or tilting the headlight unit. The headlight unit is clamped onto the three screws with the white connectors, you can now knock it out from behind with a large screwdriver. To do this, place the screwdriver next to the clamping points of the white connectors from behind and tap the headlight out with the heel of your hand or a rubber hammer.
Reassembly is not complicated, basically just the whole procedure backwards and glue with new silicone.