Side mirrors rotate all the way forward due to 2 unrelated failures. One failure is the bump cam was dislodged and then snapped into the wrong indent. To fix this, you must rotate the mirror relative to the bump cam until you find the correct indent.
The second (worse) failure is the slider pin that locates the mirror's open position becomes stuck in its cylinder, not providing the resistance the mirror motor needs to find the intended open position. This DIY addresses the slider pin failure.
One gentleman posted a video on how to fix this failure the "right" way. A big thanks to him, as I studied his video to find this workaround. Study this video to understand what the parts look like inside.
Instead of complete disassembly as in the video, after taking off the mirror shell, I drilled a hole from the top to access and clean out the spring and slider pin.
Disclaimer: I have spare mirrors. This is a hack. Perform at your own risk. This DIY is primarily to show where to drill the hole. This method worked for me but I am a hack. I don't even use BMW branded coolant.
1. Gently pry off the mirror shell, and use a trash bag or something to keep degreaser off your pretty door. Here, I have already sprayed engine degreaser around in an attempt to release the pin with no luck before deciding to drill a hole.
2. Drill a small hole through the potmetal casing from the top. You can see where I drilled and missed; the intersection of the two red lines is where you should drill to hit the center of the pin cylinder.
The center of the cylinder is 1/4" and 1/16" from the edges of the cast vertical spline as shown by the offset dimensions in the pic. Drill with a 1/16" or 3/32" drill bit.
You can see my hole was initially in the wrong spot. I used a pick to feel around and push down in the hole, but I could not get the pin down. The mirror still rotated all the way forward.
3. Enlarge the hole if need be to expose the spring and cylinder where the pin resides from the top. What you see here inside the hole is the left side of the slider pin cylinder, and the small ring is the slider pin spring in the cylinder. Fortunately, there's more than half of the "ceiling" of the cylinder left for the spring to push against. Your goal is to drill a hole inside the cylinder the first time so you can clean it out.
After drilling the hole, clean it well with degreaser and push it down with a pick. Now test your mirror--mine stopped in the correct location after this step.
4. Use an acid brush or other small brush to remove as much potmetal as you can, then pack the cylinder with dry graphite lubricant. All that shiny stuff in the hole is dry graphite lubricant. You can use grease but I thought dry lube is best here given why I'm drilling into it in the first place. If your hole is really tiny, you may be better off with a pressurized lubricant that you can spray through the hole, like lithium grease or even wd-40.
5. Cover the hole with aluminum duct tape. Make sure the outside of the potmetal is very clean--no tape will stick to graphite or grease.
6. Reattach the mirror shell. It's easiest to push on the mirror to break the bump cam, which lifts the mirror a little, and push the mirror all the way into the door to get the mirror shell back on.
Again, thanks to the original video author for explaining the failure, and I hope you find this method (though hackier) is easier than drilling out and welding the spring clamp. Good luck--let us know if this works for you!
Dan H