David Mansell, a long-time managing director at Onex Partners, is leaving the firm, reported Buyouts. The reason for Mansell’s departure is not clear but in an investor letter seen by Buyouts, Mansell is leaving in the next few weeks. Mansell joined Onex in 2002. He is based in Toronto and focuses on deals in the consumer and packaging industries. Onex also has offices in New York, London and New Jersey.