From an engineering perspective, I don't recall differential aileron on the Gnat. I could be wrong of course and stand corrected if this was the case.
I do recall changing innumerable aileron hydro-boosters however, which were prone to leakage, and likewise the Hobson Units which were a nightmare to set up once the rear fuselage had been connected up again.
I also recall the very complex "monkey puzzle " pulley box system located behind in the rear seat which gave problems for a while, but which were subsequently modified.
NON of the above should in anyway be construed as speculation however, just some clarification as to the flying control systems.