Citroen GS A Workshop Manuals
If you want to execute adjustments for your Citroen GS A then it is usually recommended to have a Workshop Manual to keep just for reference in the event you need to know how to remove a specific part much like the Clutch and match it again successfully.
Searching for Citroen GS A Manuals.....

Citroen GS A Workshop Manuals will give you identifiable diagnostic info with regards to your automobile so if something is wrong it helps you understand what the issue is and easy methods to fix it. Then you are able to determine if you can do this by yourself or in case the job is just too big you can book your GS A in to a suitable car garage.