In general in condominiums the home owner is not responsible for the main sewer line. The main sewer line is that portion of the line that starts directly outside of the structure and flows into the city sewer (or private sewage disposal system depending on the property.)
Judging from the above statements excerpted from your CC&R's it sounds like your HOA should incur the cost to repair the line. It's also important to understand that if you are having issues, it is very likely that other homeowners are having the same issues as it is very likely that any units that are in the same building as your unit have drain lines that are attached to the same main sewer line.
If the property is located in or near Los Angeles County and you are in need of a sewer line video scope, please call Sewer Line Check professionals at 818--951-7660... more