Thanks for the comments. Last week, before I did the resoldering and put in new lamps, the left lamp would go out. Without my wife here yesterday to observe, I just assumed the left lamp was still out when the bulb check light came on. But not so. Using the garage door as a reflector, I just checked and both stop lights come on okay with the key on. With the motor running, both lights come on okay, but the bulb check unit light comes on when I step on the brake (no other time). Brake lights now work fine it seems.

BTW, I have a complete set of the original M-B manuals, including the electrical troubleshooting book.

Thanks again.
Brent Smith