Using sealants on flared fittings is not wise.  A certain amount of residue is likely to enter the fuel system and hopefully will end up in screens.  If it were small enough to pass the gascolator there is a chance that it will end up in the fuel regulator needle valve in the engine driven fuel pump (on the TSIO 550).
But a better solution is not to use anything at all.  Same for hydraulics.
Much better to change the fittings, --however there are copper inserts called Flare Savers, that might be valuable if you had a fitting that had a scratch in the face of the flare.  And it could not easily be replaced.

http://www.hydraulic-supply.com/pdf/341.pdf

Charlie K.