This has been discussed before, so there should be something in the archives. My understanding is that, as a result of customer complaints of the clicking, the factory started adding some “brown sticky goop” at some point in production. Several folks here (@John_M_Holmes springs to mind) had an awful experience trying to separate the splines as a result. On my car, one side took a lot of pressure on the press, while the other side was much easier. Hence, my decision to just use a little anti-seize when I re-assembled. It proved fruitful, as I had to change out the craptastic half-shaft UJs after the first Oil Leak tour, and the splines separated nice and easy.