Thank you for these further sources for Oliver Sarazin. A few comments:
The William de Flamville who died without issue, leaving four sisters as his heirs, was of Whittingham, Northumberland, not of Leics/Warwicks. See, e.g., the IPM of his sister Constance, wife of William Bataille (CIPM vol I, 478). The Northumberland Flamvilles were discussed by Michael-Anne Guido on 14 Jan 2005 in part 2 of Ancestry of Beatrice, wife of Robert Hauley.
William de Flamville of Aston Flamville, Leics, father of Petronilla wife of Robert de Leycestre/Leicester, was referred to by MichaelAnne Guido on 6 Jan 2002 sub Reginald Basset of Wolvey, but with no further details. Nichols (Hist. Leics vol 4 pt 2) gives a pedigree of Flamville of Aston Flamville but names only William's son and heir and does not name his wife.
It is easy to confuse the two Williams, as both were the sons of a Roger Flamville (and to make matters worse there is also a Roger Flamville of Yorkshire at about this time; see Charles Clay and Diana E Greeway, Early Yorkshire Families,30, 32).
The reference to Oliver Sarazin and the sore hawk also appears in VCH Warwickshire vol VI, sub Willoughby, which states that Ralph son of Wygan "had enfeoffed Oliver Sarazin of an unspecified amount by service of a sore sparrowhawk, and Oliver had enfeoffed William de Flamvil on his marriage with his daughter Petronilla."
Thank you, and thanks also to John Watson, for pointing me to the article in Transactions of the Leicestershire Archaeological Society. The Oliver Sarazin there named, patron of the living of Shackerstone in 1220 (also recorded by Nichols), who had only two daughters, could well be a later Oliver, as the Oliver whose daughter Petronilla married William de Flamville was living and clearly of age in 1178/9 (when he purchased the wardship of Henry de Areci) and 1190, when he witnessed the Odstone charter. The article in Transactions makes no mention of these earlier records.
William de Flamville, father of Petronilla wife of Robert de Leycestre, was serving as steward to William de Hastings in the early 1220s, which is congruent with his father-in-law being an earlier Oliver Sarazin.
So my question remains, was Petronilla Sarazin, daughter of Oliver and wife of William de Flamville, the mother of Petronilla de Flamville, wife of Robert de Leycestre/Leicester? To me, it seems very likely that she was, but it would be good to have confirmation.
Saba