You might regret asking BillG. Yes he did keep a sort of written log. As I've heard and seen the story, he always kept a small spiral flip notebook on him to jot down ideas that came to him, wherever he was. Then at night, before bed, he would transfer those ideas to a 81/2 X11 spiral notebook on his desk at home. As the story goes, when he died, he still had 200 ideas in that notebook at home that he had never gotten around to.
Another story my dad told me at dinner the other night was about the old Tournapull factory in Peoria. Coming out of WWII, the Tournapull was the hottest selling machine that RG made. It was the old original style that had the clutch steering that is similar to the steering on a dozer. Well, in the early 50's I believe, he had designed his first electric steering model Tournapull, which he thought was far superior to the old clutch steering model, but it wasn't selling. He couldn't understand this and blamed his sales force for not making customers aware that the newer model was superior. This was back when RG LeTourneau Inc was doing $30-40 million a year in sales after the war. Well, not always being the smartest business man, RG shut down production of the older model Tournapull at the Peoria Plant and only produced the newer electric steer model, even though he had not really worked all the kinks out of the new model. Sales at the company plummeted and he nearly went bankrupt, but they survived and sales eventually picked up. As my Dad tells it, that was when some of the senior management at the Peoria plant began looking around for a buyer for their operation which eventually turned out to be Westinghouse Air Brake Company and led to my grandfathers exit from the earthmoving machinery for a number of years.
While my grandfather was brilliant in many ways, he was quite eccentric and dictatorial in his style and relationships. He fired my dad once in the 60's for suggesting that he "retire". I have great admiration for much of what he did and a passion for his machinery, but the man had serious flaws as well. In a way that is comforting to me, being brilliant and successful doesn't mean you have to be "perfect".