There should be a copper washer on each side of those 'banjo bolt' fittings, one on the head side, and one on the other side.
Tightening really should work. The copper washers do all of the sealing here, though they must be flat and clean. This is not a place where you can add sealants, or teflon tape, or the like...
See image at:
http://www.eccentrix.com/computer/csnow/images/MBFP.jpg