MILAN/LONDON, June 20 (Reuters) - Fiat's creditor banks favour the sale of the group's core car unit Fiat Auto as it struggles to curb debts and losses, sources involved in the talks between Fiat and the banks said on Thursday. The sources also said Fiat was prepared to sell its insurance arm Toro -- which is estimated to be worth nearly 4.0 billion euros including goodwill -- if it did not meet financial targets this year.