21 mmHg does not means a leak present, In fact it is perfectly healthy and your rings are sealing. I'm willing to bet there isn't even a leak anywhere. How does your idle RPM look like when warmed? And what was the CEL related to?

I have yet to hear a case of Boost gauge install yielding a CEL when performed correctly.

If you had a leak in your vaccum source, your numbers wil be lower (meaning toward zero), and your idle will be higher. Plus you woudl hear it too.

-K-