Robert Weil is a son of refugees, a patron of the arts and an ardent campaigner against social inequality and nationalism. He is also a billionaire financier who knows the importance of shoring up an investment portfolio when the need arises. And in recent times, the Swedish tycoon, by his own admission a contrarian investor, did just that. His target? A Dublin aircraft leasing business with liabilities stretching to more than $100 million. Proventus Capital Partner, Weil’s investment giant, is one of the main backers of Montrose Global Aircraft Management (MGAM), a Dublin firm that leases small planes to small,…