I just bought the complete Set (1978 to 1982) on DVD. (I can't believe how much the price varies on the net - I paid about A$77 including postage; other places had it for about $100 more!)
The DVD picture quality varies enormously between the 1978 and 1980 episodes, I presume that would have been due to poor archiving, since it must have been shot on 2" tape, which normally holds up very well even 40 years later.
There was an earlier release of this series, but due to music copyright problems it had to be severely mutilated and didn't sell very well. In this latest version by ShoutFactory they say they managed to recover about 80% of the music.