Complex sentence: His spell with the "Dark Blues" was less successful however, and following their last-day relegation in 1975-76, ironically only by virtue of an inferior goal difference to former side United, he retired aged 32.
Split into simpler sentences: His spell with the "Dark Blues" was less successful, however. Following their last-day relegation in 1976, due to a goal difference inferior to his former side United, Gordon retired from football aged 32.