Does it leak that much around seat edge?... small bubbles would indicate a seepage around the insert, but I'd be surprised if it caused any issue with the engine running... The only concern would be if its a shrunk in seat ring, then it could drop out, but usually they are cast in and are fully captured.

Try Berts suggestion, red loctite or the loctite Bearing retainer, which should wick in under a vacuum for sure, good idea actually.