Okay I received the part, well actually 10 of them, ETC8833 is the exact copper o-ring for the relief valve plug. However, when observing the leak I noticed I had a front main seal leak too. Bummer, because it was new and pretty sure it was a Genuine LR part. It ended-up having a small tear. Not sure if that was my mistake or I just missed when I was doing the top end rebuild. The harmonic balancer had a little wobble too, but barely noticeable for so many pulleys stacked together.
So, I set off to replace the copper o-ring, front main seal, and swap the balancer. I bought a new balancer from Atlantic British, but I ended up having to pull one from my parts truck with half the mileage. The one AB sent has too short of a snout and the timing marks are clocked way off. Yay.
Popping the old seal out with a taped screw driver was easy. Putting the new one in with the cover on the truck was horribly time consuming. I ended up using the crank bolt with a balljoint press cup, which of course bottomed-out against the crank nose (4.6) mere millimeters from where the seal needed to be. So, I engineered a slightly longer cup with a PVC coupling and a cap.
After that hurdle I went to I went to disassemble my pulley stack to swap the new balancer in just to notice it had WAY too short of a snout to work. It says it fits 89-95 RRCs, but it sure doesn't match the 91 parts truck's or the intended recipient 92's. Thanks Atlantic British!
Well, now I had to remove the balancer from the parts truck. The bolt wouldn't budge so, on top of the belts and PS pulley, I had to pull the radiator to get my M18 impact on the bolt. Fun times. Oh, and the donor balancer was a pain too because the mating surface for the pulleys was rusty. Had to press them apart and back together with my stack. I have a funky v-belt + tiny ribbed alternator belt set up on the 4.6. I honestly hate the multibelt setup even more after this fiasco.
Here's some pics of the old, donor, and "new" crank balancers.
I carefully loosened the plug with a 26MM so it didn't rocket out from spring tension. Lost a handful of oil quick swapping the o-ring but it's in there now, along with the new seal and better balancer. It could've been worse but man these v-belt/distributor trucks are just archaic to me. Makes me want German cars again.