I buy most of my parts from the dealer I bought the jeep from, got a 20% discount from them. One friday I was headed home and stopped to pick up the standard tune up parts, he only had 4 of the plugs so I got those and stopped at a parts store to pick up two more. When I got home and was pulling them out to gap them the two from the parts store were different, thinner electrodes, thinner ceramic, same part number but different, cheaper to my eye. Was it a fluke, don't know, just know I have never been burned by the dealer with parts that don't fit or don't work right.
Now I get my parts from the small local dodge dealer once I found out he can order whatever I need and he gives me the same discount, all I have to do is take the vin in with me. I have also been sending all the local jeep owners to him for parts to the point that he now keeps a pretty respectable jeep parts inventory for TJ's and XJ's for normal items and he gets stuff that needs to be ordered in 1-2 days, probably from the same warehouse as the jeep dealer. Difference is I don't have to drive an hour there and back...
As for those two oddball plugs, when it came time to change them again next spring the gap on the 4 OEM plugs was like .050, the gap on the two oddballs was .060-.065 and they were carboned up badly.
I'm also one of those who buys most of my stuff from the dealer. I use Mopar anti-freeze, belts, hoses and until I switched to mobil-1 I used mopar oil filters too, bought a case of them when I picked up the jeep new as well as the FSM. I tried purolator oil filters twice but they took too long to build up oil pressure on morning startups and after I finished 8 hours at work which I was not comfortable with, mentally counting to 5 for the oil light to go off when I had my idiot light dash bothered me no end. Never had that issue with Mopar, Mobil-1 or K&N filters. I did have K&N filters loosen up on me a couple of times and they were put on tight, I use one of those oil filter sockets and a ratchet so I know they were not loose to begin with...tried them again this past summer and the problem has not come back so it might have been the material they used on the O ring. All three of our jeeps and the wifes Oldsmobile run mobil-1 as well as mobil-1 or K&N filters, when they go on sale at the local AA or National auto I stock up.
Reminds me, gotta stop at the dealer today and order a PS pump and fan shroud, plus some other odds and ends for my sons TJ and my daughters TJ...the 4" suspension lift and 2" body lift are going in this week.