Glad you were still able to get the brush hog up and running. We just settled into our 10 acre farm last month and I spent the first two and a half weeks "brush hogging" with a Cub Cadet 2166 riding lawn mower because I do not own any implements or tractors yet. I put my little Cub through hell and luckily it did the job!
Wondering if after you are finished using the brush hog if you stand it up and just keep soaking the spline with diesel fuel for a week or so. Then make another attempt at it. I used diesel as a penetrating fluid when I was in the Corps. Always did the trick!
Good luck!