1. Use the reservoir from your old clutch master. Clean it with some bleach water.
Or:
2. Remove your leaking reservoir and clean it thoroughly with hot water. Let it dry. Put masking tape on the outlet, mixup some JB Weld and pour it in until it is above the riveted ferrule. After the JB Weld is hardened, drill it out. Brake fluid does not affect JB Weld.
Or:
3. Get a new reservoir from Wilkinson. He has a bunch of them.