Oil cooler question

I gather from the post "Oil cooler time" that these trucks came with an oil cooler. Is it located under the driver side exhaust manifold? Kind of a dumb place, isn't it? I was thinking about installing an oil cooler until I read about the factory one. Do they work very good? How often do they need to be taken off and cleaned and where do you get the O-rings? Is there any way to do away with it and install an aftermarket one infront of the radiator?

Also, how often does the fuel filter need to be changed?

Thanks

Trevor in MO