When did the half hourly Buxton service finish then? I can only remember the hourly Buxton and hourly electric shuttle (not exactly infrequent or irregular) before 2008. Indeed the hourly electric service to Hazel Grove was the best place to find the remaining 305s and 309s in the late 90s.
Until October 1990, after which Buxton went back to hourly but Hazel Grove got two terminators per hour - each coming through from either Wigan Wallgate or Southport. So although Buxton lost out, Hazel Grove got an improved three tph (none of them using the wires!)
When I said "infrequent and irregular" I only meant compared to the regular, hourly, all day EMUs to Hazel Grove. After the Windsor Link opened, and then later when Altrincham went over to Metrolink, the Hazel Grove terminators were often diesel for various reasons, and those that were EMU operated became fewer and at irregular times (and often changed with each new timetable.)