I believe that the part number of the grommet that I used is 113-611-817A. It's listed as:
VWC-113-611-817-A - BRAKE MASTER CYLINDER RUBBER PLUG - SECURES INLET PIPE TO CYL.- MEASURES 11MM INLET / 24MM O.S. DIA. - BEETLE 72-79/GHIA 72-74/ THING 73-74 / VANAGON 80-91
These grommets were a very tight fit. I used brake fluid on the grommets as a lubricant, placed a block of wood on top of the reservoir, and used a c-clamp to compress. Carefully tighten the c-clamp and wait a few hours or over night. Carefully tighten the c-clamp again and wait. Repeat as necessary.
John