Originally Posted by ChrisSlicks

The issue you then run into is that it becomes difficult to get an accurate oil-level reading. Every time you shut off the car the oil from the cooler drains back into the sump throwing off your dipstick reading.

It might be possible to get a skilled machine shop to add a drain plug fitting to the bottom of the cooler, you would just have to take care that it was properly re-torqued so as to not become a potential point of failure.