Current restoration is good; could be better
The currently playing restoration of Becket, which was in fact completed several years ago, required a significant amount of effort and money to accomplish, mostly to put together a new interpositive from the separation master, and to rescue the multitrack stereo soundtrack from serious physical deterioration of the available magnetic analog masters. You can read a bit about the restoration process at http://www.becketthemovie.com/becket_00.html.
There are four things I noticed, however, that could have been done better, and not necessarily with a great deal of extra expenditure.
First, there is an audio continuity error in one scene where Becket is chanting in Latin, and the pitch of his voice goes down a semitone from one shot to the next (something that as good a singer as he seems to be would essentially never have a reason to do in real life). This could have been corrected in a matter of minutes, by digitally lowering the pitch of his voice in the first shot.
Second, there is one scene where the colors fluctuate wildly for a minute or so, I suppose due to deterioration of one or more of the separation master elements. This could have been digitally corrected, I assume with a few person-days of labor at most.
Third, the film sounds as if, in the original final stereo mix of the soundtrack, the volume was subjected to some kind of compression or limiting, presumably as a concession to the inadequate amplifiers and speakers that were often in use in even some of the better stereo-equipped theaters of the 1960's. As a result, the dialogue, sound effects, and music never hit the volume peaks you expect them to: instead, they repeatedly wimp out at the climactic moments. It would have been nice if the restorers had done a little tasteful re-expansion of the soundtrack volume, so as to get rid of that unfortunate relic of a comparatively backward era in cinema audio.
Fourth, the soundtrack is a bit deficient in the bass frequencies, which again was probably done in the original final stereo mix to protect inadequate theater amplifiers and speakers from damage. Some tasteful re-equalization of the soundtrack would have been nice.
I wonder whether there's time left to correct some or all of these problems in the upcoming DVD rerelease.