Coil made at least three references to his being unhappy at JFR. If I recall, John Medlen had similar feelings, although he wasn't as vocal about them. That doesn't mean John necessarily did something wrong. It could be Castrol, or Ford, has scaled him back. Maybe he had to cut expenses, or personnel, in ways that Coil didn't feel comfortable with. And I see a slow change in personalities - with Austin wanting to slow down a bit, and John wanting to throttle up.
Coil, being the professional that he is, is honest enough to speak out with nothing but praise for his longtime friend and partner, while at the same time letting everyone know it's just time for a change. As I said earlier, I don't believe this was a snap decision. Saying so long won't be easy for him, either. A 26-year relationship doesn't end overnight.