No previous issues. The castrol fluid listed Atf+4 as a suitable replacement.tellya what I think.. electronic controlled tranny's are designed around the fluid's characteristics nowadays, and unless nothing else is available its best to use the recommended fluid... in your case you didn't mention if the transmission had any previous problems or had been previously serviced but it is quite possible that new clean fluid reacted with the other stuff that is always left behind and caused some problem which evidenced itself 15000 miles later but know way to know for sure but it isn't like the old days when tere were 2 kinds of fluid..
I had serviced the transmission prior 1 time with super tech ATF+4 at about 60k.