From 1957 to 1959 he was vice dean. In 1965 he became professor with a full lectureship for music history, instrumentology and folk song studies at the same university, from 1965 on at the , department of music education. In 1966/67 he was head of the department of artistic practice at the institute. In addition, he was second chairman of the Senate Cultural Commission of the University. In 1967 he became Emeritus. From 1947 to 1967 Willert was member of the . From 1960 he belonged to the , the and the Gesellschaft zur Verbreitung wissenschaftlicher Kenntnisse (Urania). From 1961 to 1967 he was on the Leipzig district board of the Urania. In 1972, Willert moved to the Federal Republic of Germany to Dietzenbach-Steinberg (Hessen), where he was the representative of the organist in the Martin Luther Protestant congregation. From 1981 to 1986 he represented the organist in the Evangelical Lutheran parish of St. Peter in and in the Evangelical Lutheran parish of the monastery church of St. Nicholas in Göttingen-Nikolausberg. In the FRG he published numerous introductions to works and operas. Willert died in Göttingen at the age of 86.