Yes I run a shop. I also own and have owned many vehicles with Ford 4.6 engines. My mother, step-father, aunt, uncle, and grandmother all drive panther cars with the 4.6. I have a limo fleet as one of my clients, who up until recently was running 7 or 8 Lincoln town cars, all with the 4.6. This doesn’t even get into the 4.6 powered vehicles owned by many other customers. I have had more 4.6 intake manifolds off than I can count, both OEM and Dorman. The simple fact is that they all fail. The original all plastic ones cracked the crossover. The aluminum crossover ones crack between the plastic manifold and the aluminum crossover where they use integrated gaskets. The Dorman ones fail at the integrated gaskets both between the head and the plastic manifold, as well as between the plastic manifold and the aluminum crossover. They are all made of plastic, and have coolant circulating through them, so they all fail. The OEM ones seem to generally last 10-12 years. The Dorman ones generally seem to last 4-6 years. There are obviously exceptions in both of those groups. I have seen OEM manifolds that were 20 years old and not leaking, including one 99 Mustang with the all plastic crossover that as of a few years ago was still just fine. I have seen OEM ones that were 6 years old and leaking. I have seen Dorman ones fail in as little as 2 years. The OEM ones use better quality plastic, but it is still plastic. If you want to buy one intake manifold and never have to worry about it again, spend the $600 for a typhoon all aluminum one. If that is too much, buy the FRPP one for $300, and you should be good for 10 years. If that is too much, buy a China aftermarket one, and you might get lucky and have it last, but don’t be surprised if it fails in a few years. As for a used one, mosy of the used OEM ones I have pulled off were either already cracked, or about to crack at the crossover, so unless you know it was recently replaced, I wouldn’t bother with a used OEM one.