Helllo Steven, yes the Sinn Navitimers are pretty common, perfectly legit and indeed excellent value for money: the one I am referring too is one specimen that had both (!) brands on the dial, just one on top of the other...
Cheers,
Fabrizio

:When Willy Breitling sold the company (trademark) to the Schneider
: family in 1979 just prior to passing away, he apparently also
: sold some inventory of cases and such to Helmut Sinn, for the
: Navitimer. There was an arrangement whereby Sinn was/is allowed
: to produce a variant of that 1970's Navitimer under the Sinn
: name. So, not an issue here of Sinn simply adding their name to
: watches in for service. They are officially allowed to produce
: that one variant (same case style and dial minus the Navitimer
: and Breitling name), it is their Sinn 903 model which sells
: direct for a very reasonable $3,310 which I just checked out on
: their website. Pretty reasonable considering the current
: Breitling Navitimers list for north of $7,000.
: Steve