If its a rubbed pinhole in the low pressure side, a brazing rod for aluminum repair will probably work fine to fix it. Look at Aladdin 3-in-1, or Durafix. De-contaminating the repair area will be key. All the PS fluid will need to be gone from the repair area. Get a small, brand new stainless steel wire brush and follow the cleaning instructions that come with the rod. It will be a process of heat, brush, heat, brush, braze, brush, etc. Build thickness, don't worry about making it look pretty.
These rods are regularly used to fix damaged A/C and refrigeration aluminum evaporator coils with good (but not 100%) success. The system pressures would be similar between the return side of a PS system and medium temp refrigeration evaporators.