Greetings, I didn't check with NAPA or anyplace like that, I have been led to believe teh orings are a Ford only part. The gaskets are supposed to be available at any good auto parts house. i got teh whole mess of it at Ford, I just haven't picked them upa nd done teh job due to writing papers for school and doing research to find the best method. Yes the cooler bundle reaches from the oil filter header up into the engine block, it enters the engien block by the drivers exhaust manifold. I was told to do this job 24K miles ago when I had the heads off for head gasket refresh, but it wasn't leaking then and I was deep in debt....I would say yeah, it works very well, better than nothing anyway, anythingto help deal with the extra heat of a diesel or the stress on any heavy duty vehicle like that. You may or may not know these things also have piston cooling oil jets that squirt oil on the piston skirt. Thus cool oil is a big part of keeping these trucks alive in severe service. You might say that the oil cooler, and the jets, are a big part of how come everybody who has exceeded 1250*F EGTs even for a second doesn't always melt down their pistons immediately. As far as frequency of service...my truck just flipped over 177K miles and I believe teh oil cooler and O-rings to be original, mine hasn't dumped the oil pan on the ground yet, nor has it put any visible coolant in the oil or oil in the coolant, but the bundle now leaks a good bit of oil. From what I hear 175K miles is about average for the lifespan of oil cooler orings, but they may fail more from just plain old age or improper cooling system maintenance. Good luck, I will let everybody know how my overhaul goes.