The 123 car has no electric pump as do many other models. Start with a hand vacuum pump at the vacuum connections going through the firewall near the oil filter. See that it holds vacuum there. It probably will not. If not, split the circuit by starting at the passenger front door. At that diaphragm, remove the line that goes OUT of that diaphragm toward the back door and plug its connection on the diaphragm. If both front doors work well then the problem is in the right rear door, fuel door or trunk. If they still don't work then work your way back toward the firewall.

This is very simple troubleshooting and you start in the middle and work toward the problem.

Good luck,