Well, I may be wrong, my wife tells me I am all the time, but it is my belief the Groetchen Columbia was basically the same internal mechanism in all their models including the Gold Award model with the addition of the Gold Award dispensing assembly!
So most manuals, Etc. cover all models such as the Dick Beauschel book number 19 shown below which is available for download at Rodger "Jackpots" web page linked here below
http://www.coinslots.com/manuals/Granted the coinhead was either a "straight drop" design as shown below or a "circular head" design also shown below but I believe the internal main portion of the mech was very similar in all the models with the exception of the Columbia Chrome Bell which was a larger version of a similar mechanism!
Below there is also a pdf of an article written in the Coin Slot Magazine of January of 1982 on them as well for you to read!
A photo of yours showing the area of your issue may be helpful for a Groetchen Columbia collector on the site to help you further!
Hope this may help!
Bona Fortuna!
MONTI
BOOK #19 on the Groetchen ColumbiaCOIN SLOT Magazine Article of 1982
Straight Drop Coin Head
Circular Coin Head