Thanks for the reply, dkveuro.

I went to the dealer today and ordered the oil cooler/block associated o-rings, and the gasket that goes between the filter housing and block. I should be set for whichever scenario I run into. I'm going to try removing the oil cooler by itself before removing the filter housing. If the filter housing has to come off so be it. I'll have the gasket in hand in case it's needed.

I found this thread:

http://www.peachparts.com/shopforum/diesel-discussion/334961-oil-filter-housing-shaft-o-rings-size.html

In post #13 there's an attached image of the oil cooler/filter housing which I assume came from the EPC. It matches the image I saw while at the dealer's parts counter today. I ordered #278 X1, #275 X1, #284 X2, #263 X2, and #230 X1.

Anywho, looking at the diagram makes me think I could remove the cooler without messing with the filter housing, replace the o-rings, re-install, and be done. Seems possible unless the cooler needs to move in a direction it can't while filter housing is attached to the block.