When I was a kid (probably in the early 1980s), I borrowed a pair of LPs from the local public library, each of which told the story of one of the mightiest knights of the Round Table: first Lancelot and then his son Galahad. Those were the only records that the library had from that particular series, but I remember having the impression that others had been published, featuring other Arthurian tales. I also think that the records were based on a printed book or books. I remember the two album covers having an azure background field, with sable line art depicting Lancelot and Galahad, respectively. I would like to locate these stories again (especially Lancelot's), either as recordings or in book form.
The story on Galahad's record was pretty familiar to me, as it was mostly the Grail quest. On the other hand, Lancelot's story had a lot of elements that I had never encountered before. The record spent quite a bit of time on Lancelot's adventures before he joined King Arthur's court. In particular, I remember quite vividly a segment where Lancelot saves a town that is being menaced by a horrible worm-like monster, which comes out at night to eat people, before withdrawing underground during the daytime. (I envisioned as a giant gray annelid, but I don't know if that was from the narration, or an image I came up with on my own.)
Later, the record told of how Lancelot joined the Round Table. At a tournament, Arthur's forces were lined up against those of another lord, and Lancelot (who arrived at the tourney late) decided to join whichever side seemed to be losing. Once Arthur's knights had shown their superiority, Lancelot entered the fray on the other side and turned the tide. Arthur was naturally impressed with Lancelot's skill and offered him a seat at Camelot.