OEM seals are invariably better than the aftermarket. The OEM will spend more money on no leaks especially with extended warranties. I have seen rear seals in aftermarket rebuild kits using silicon when OEM is at viton because the silicon is significantly cheaper. The Fluoro elastomer is an order of magnitude better in a 4.00" dia seal where the shaft speed ininches of movement per second is much higher. The front seals on the 2.3 and most lip seals on the wheels and axles are Nitrile, which is not nearly as good as Viton, but with the small diameter of shafts it usually more than acceptable. The European sealing community still believes in Nitrile or hydrogenated nitrile. To answer Bill and Brads question though, I would use the factory Nitrile. The factory front seals of the 2.3 are dual lip Nitrile and have been from introduction in 1974. I tested and released Viton material, but failures of front seals were seldom seen except at high mileage. The viton part is E6ZE 6700 AA. Sorry brad I left that out of the original note. Actually after the earlier note I checked my records and find that I have been using the E6ZE seal which is Viton. Use this part from Ford. The color of the elastomer is brown, and there is a green coating on the outside of the seal. It is called bore tite. It is a glue/sealer that helps the bore OD sealing. All of the production engine seals are Chicago Rawhide. The chassis seals are probably Freudenburg of Germany and the color of the elastomer is black. Buy the seals from ford. Now that I am interested in the last Inch ounce of friction, I am switching to a PTFE (Teflon) engine rear seal of a slightly different design. If it is worth .01 MPH I'll take it. We do not need that for the street though. And without a dry sump for sureyou dont need it.
Front crank, cam and auxiliary shaft seals are the same. Buy only factory or a source that sells you the OEM Chicago Rawhide seal. When going away from factory the aftermarket becomes so competitive they will sell you something else. Even the same manufacturer of the OE part. A small change of material can mean a difference in life of the part. D42E 6700 AA