Add the following adjustment procedure to the 1989 Pontiac Lemans Service Manual, page 2T-7.
This vehicle's inside rearview mirror pivots at two places; the ball-and-socket mirror pivot and the fore/aft hinge pivot located at the window base. Only the fore/aft hinge pivot is adjustable. If the ball-and-socket pivot ceases to function properly, replace the mirror assembly.
Adjustment
* Insert a 3mm Allen wrench into the adjustment set screw on the right side of the window-base pivot.
* Loosen the set screw and move the mirror to the desired position.
* Tighten the set screw to retain this mirror position.
It is possible to leave this set screw slightly loose to allow the driver to adjust the mirror while driving. However, over time the screw may loosen further, causing the mirror to drop below the desired adjustment height. If the vehicle's owner requests this type of adjustment option, instruct him or her on how to retighten the set screw should it loosen in the future.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.