try to find out were the oil leak is come n from

That round piece is the adaptor for the oil cooler lines and the tubes going out if it are the oil cooler lines which go to the radiator. The adaptor plate or the lines could be leaking.

perhaps your engine oil cooler tubing o-ring seals; engine oil cooler seal kit

oil cooler attachment(normally the oil filter would attach here but for the transfercase would be in the way