My alternator decided to stop charging the other day. The dreaded red warning message showed up intermittently for a few days, after which it became permanent.
I suspected the regulator, so I got under the car and removed it through the back.
Tiny screwdriver and nut driver were extremely helpful.
One of the brushes was worn out and wasn't making contact anymore.

Original regulator would have cost me $148 + tax at the local dealer.
I found the same part online for $50 and up, including shipping.
Decided to keep looking.
I contacted some local alternator rebuilders. One of them offered a VR (not Bosch regulator) for $25, and a free brush to replace the broken one.
I fixed my old regulator and installed the VR one.
If you're facing this problem and you have one type of regulator (in my case Bosch), don't be afraid to try a different one (like VR), as long as it fits mechanically.
After all, they all perform the same job: adjust your rotor current so the charging voltage stays between 13.5 - 14.4V. The only variable as far as I can tell is the current driven through the rotor.
I hope this helps someone.
Tudor