I usually prefer external coolers, instead of coolers that only cool the oil to the same temp as the engine coolant. What if your engine overheats?
I think that if you get a good sized external cooler, you should be fine. Plug the holes going into the radiator, just in case.
Another reason I prefer external coolers, is I had one of the internal ones leak on me - a new radiator and transmission later, I was back on the road.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D