JOHN, son and heir, was presumably born before 1056, for about 1076 he suddenly claimed and seized the mill of Vains, but after a trial before the King's Court judgement was delivered against him. As John son of Richard he gave the tithe of Saxlingham, Norfolk, to St. Peter's Abbey, Gloucester, in the time of Abbot Serlon (1072-1103/4). In 1086, described as John nepos W., he was a tenant-in-chief in Norfolk, his estates including the manor of Saxlingham to which the church was appurtenant; and as John nepos Walerami (sic) he held also the single manor of Elsenham ("Alsenham"), in Essex, in chief, and a carucate and a half at Saxlingham of the abbot of St. Benet of Holme. He is said to have been given the advowson of Hockham, Norfolk, by Roger Bigod (died 1107). Nothing is known of his marriage, death or burial. [Complete Peerage XII/2:269-70, (transcribed by Dave Utzinger)]
Note: In Appendix B, Vol XII/2, the Complete Peerage gives evidence and a lengthy discussion, disproving a long held belief that John was brother of Serlo de Burg (and therefore son of Eustace de Burgo), whom I originally had as his brother. CP also states that John's son Eustace FitzJohn was called Monoculus, possibly as a hereditary nickname from his father, but potentially in place of his father.
-----------------------------------------
John, surnamed Monoculus from having but one eye, had three sons, Paganus, Eustace, and William. These brothers were witnesses to the foundation of the abbey of Cirencester, co. Gloucester, 1133. The elder son, Paganus, dying s. p., was s. by his brother, Eustace Fitz-John. [Sir Bernard Burke, Dormant and Extinct Peerages, Burke's Peerage, Ltd., London, 1883, p. 121, Clavering, Barons Clavering]