Question: What number season was the Brazillian central defender signed, who was previously a left back?

Context articles: Orhan Ak
Dante (footballer)
Andreas Dahlén
Liassine Cadamuro-Bentaïba
Kamiar Ghanbari
Darío Rodríguez
Michael Simpkins
Michael Kay (footballer)
2012–13 FC Bayern Munich season
Ziaeddin Niknafs

Orhan Ak (born 29 September 1979) is a Turkish former professional footballer who played as a defender.
 He played as a left back or a central defender.
Dante Bonfim Costa Santos (born 18 October 1983), commonly known as Dante (] ), is a Brazilian professional footballer who plays for French Ligue 1 club Nice.
 Primarily a central defender, he has previously also been used as a defensive midfielder or a left back.
Andreas Dahlén (born 11 December 1982 in Gävle) is a retired Swedish footballer who played as a defender.
 Dahlén is a defensive specialist and can play at left back, central defender or defensive midfielder.
Liassine Cadamuro-Bentaïba (born 5 March 1988) is an Algerian professional footballer who plays for Swiss club Servette FC and the Algeria national team.
 A versatile defender, he can operate as a right back, central defender or left back.
Kamiar Ghanbari (Persian: کامیار قنبری‎ ‎ ; born 1988 in Tehran) is an Iranian football defender who currently plays for Persepolis F.C. in Iran's Premier Football League.
 He is a talented left footed defender who can play in the left back and central defender position.
 He has represented Iran in most youth levels.
 He left the PAS Tehran F.C. youth system at the beginning of 2007 at the age of 19 after being approved by Hamid Estili he put pen to paper to a contract keeping him at Persepolis until 2010.
Octavio Darío Rodríguez Peña (born 17 September 1974 in Montevideo) is a Uruguayan former footballer who played as a centre back or left back for Peñarol.
 He was capped 51 times for the Uruguay national team.
 A versatile defender, he was capable of playing "at left-back or as a left-sided central defender.
 Strong in the air, he [wa]s a useful distraction in the opposition box at set pieces."
Michael James Simpkins (born 28 November 1978) English footballer who plays for Belper Town.
 A defender by trade, Simpkins was primarily a left back but now plays in the more familiar role of central defender.
Michael Joseph Kay (born 9 December 1989 in Consett, England) is an English former footballer.
 He usually played in the right back position, but could also play as a central defender and has been known to fill in as a left back on occasion.
 He is a former England Under-17 international.
 He is no relation to former Sunderland defender John Kay.
The 2012–13 FC Bayern Munich season was the 114th season in the club's history and the 48th consecutive season in the top flight of German football, the Bundesliga, since the promotion of the team from the Regionalliga Süd in 1965.
 Before the start of the season, Bayern signed Xherdan Shaqiri, Dante, Claudio Pizarro, Mitchell Weiser, Tom Starke and Mario Mandžukić.
 Bayern also added holding midfielder Javi Martínez after the first week of the Bundesliga season at the transfer deadline.
 The club started the season with a nine-match winning streak.
 The club would end the season claiming the Treble, winning the Bundesliga, the UEFA Champions League and the DFB-Pokal.
 Bayern are the first German club to achieve the Treble and are the third European Club to complete the Treble in the last five seasons and seventh ever in European Club competition.
Ziaeddin Niknafs (Persian: ضیاءالدین نیک نفس‎ ‎ ),(born 19 September 1986 in Sanandaj) is an Iranian football defender who currently plays for Sanat Naft in Iran Pro League.
 He is a young left footed defender who can play as both a left back and central defender.