Hi All,  Air motors that 'lope' are very common.  The problem develops
because the motor has been setting idle in one position for too long.
This is well explained in my web page "The 360 Degree Test".  See:

  http://www.player-care.com/360_test.html 

On that page I also offer a few suggestions which might help delay the
replacing of the old cloth.

Musically,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA