Of all the acoustics Glen has played in his career, the Martin D18, that he used in the early 60's, as a session musician, appears to have been one of his favorites. One of the stories told is that in the early/mid 60's Glen was playing golf with a guy that pulls a Martin D18 out of his trunk in the parking lot. The guitar was damaged. Glen took the guitar and had it repaired. He then used it exclusively in the studio, while with the Wrecking Crew. I have seen other stories on how he acquired it, so how Glen came about owning it is unclear. What is clear, is that this is a guitar that Glen obviously decided was a keeper.
Here is Glen in the studio, at Capital, using the Martin, June 1st, 1967.
You can watch it being played in the "These Days"
Glen recently had his picture taken with it, in 2013.
and another picture taken at his home in Malibu on the staircase: