Beyond the list of standard restoration steps detailed on the main page, here are some added notes for this unit :

I bought this locally.  It was accurately described as highly functional, but with cosmetic issues (details below).  I have always heard good things about the Sansui xx1 series (331 through 881) so interested in getting this one on the bench.

Interior was very clean and initial confirmed functionality except FM not in stereo.  Noted 12V supply instability and replaced the pass transistor in the power supply to resolve the issue.  

Aligning the tuner brought back FM stereo and the stereo channel separation is now excellent.

Listening tests showed this 551 to be a truly fine sounding receiver.  The power output is modest, but it will cleanly drive any reasonably efficient speakers to very loud sound levels.  

While functionally and sonically solid, this receiver does have significant cosmetics issues that are reflected in the price (please see photos).  The faceplate is nice except for a scuff on the bezel trim (right vertical) and scratches on the top surface.  The wood-grain patterned vinyl wrapped cabinet top also has some marks on the top and along the right edge.