This tip is from a ex Trailways bus driver on the r/h mirror adjustment on our GMC coaches.
One trick which always works for getting the right hand mirror is once you
have it adjusted just like you want it, turn on the driver's light just
behind your head.
Then, get out of the bus and stand immediately next to the right front axle
spindle, i.e. the center of the right front wheel.
Look at the right mirror. You will see the driver's light shining back at
you. Remember the exact position the light occupies on the mirror face.
Any future time the mirror gets out of adjustment, just turn on the driver's
light and then, remaining outside, adjust the mirror head so you've put the
driver's light reflection in that same position.
When you get back into the bus, your mirror will be perfectly adjusted
without ever having to play the front step shuffle.
Merry Christmas GMC Coach owners.