Are there (small) differences between the vipassana meditation technique of U Ba Khin and S.N. Goenka?
From many of S.N. Goenka's writing it is implied that U Ba Khin gave explicit instruction not the change anything regarding to the technique and I believe this is the case. Also many times in this writing S.N. Goenka has expressed profound and deep respect to his teacher. So it is unlikely there would have been any changes.
Since U Ba Khin died some time back, while S.N. Goenka taught based in India while U Ba Khin this would only be known to someone who was a student of both masters if at all who might be surviving would be very few who would know the this for sure.