Marcel Dupré improvising on the gregorian theme Veni Creator Spiritus on his instrument in St Sulpice. He clocked up 37 years as titulaire, though this is nothing compared to his teacher Widor, who managed 63 years in the post, leaving when he was 89! It should be noted however, that Dupré was a mere 75 years old when this recording was made :-)
The chant Veni Creator Spiritus (Come, Holy...