 Manager Tom Johnston was then replaced by Mick Buxton, though Armstrong continued make progress in the first team, starting 15 league games in 1978–79, and scoring once in a 2–1 home win over Bournemouth on 13 March.However he did not feature at all in the title winning 1979–80 campaign, and was also absent throughout the 1980–81 season, before signing with Fourth Division Port Vale in February 1981.Armstrong made 17 appearances for the "Valiants" at the end of the 1980–81 campaign, and claimed goals against Hereford United and Peterborough United.