Braniff Inc. has leased 10 Boeing 737-200 aircraft from Polaris Aircraft Leasing Corp., with delivery scheduled between next month and March of 1988 . . . W. R. Grace & Co. said it has agreed to increase its ownership of National Medical Care Inc. to about 80% from the current 49.9% at a cost of about $67 million . . . Chase Manhattan Bank in London has agreed to repay Colombia $13.5 million stolen four years ago through computer fraud, a Colombian official was quoted as saying.