If the turbo has been leaking oil and the oil has gone in all the pipe work , the best advice is service exchange turbo ,new oil supply pipe or seals ,oil return pipe and gaskets ,new turbo to cat exhaust gasket, you need to remove all pipe work and clean it ,if the inter cooler has oil contamination ,new cooler , and last of all engine oil and filter ,sump washer ,not a cheap job iam afraid but if you dont do something about the engine could run on its own oil ,and cause engine damage , then it will mean a replacement engine as well , hope that helps .
mark
April 2008