Is the US first season confirmed as being mono, as listed? This seems odd when seasons two and three are currently listed as stereo, as are all three seasons of the German DVDs.
It should be noted that the German DVDs have NTSC-PAL transfers.
The US sets were repackaged and reissued as "The Complete Series" box set, ASIN: B01HPGE9LC.
All three seasons were also issued in Oz by Umbrella Entertainment.