O-ring uncompressed is 0.141in thick per my mic, might be a few tenth thicker but pretty much there. It sits loose in the center of a housing groove that is 3.166in ID and 3.602in OD.
You can definitely feel the housing bottom out against the block when you tighten it up so the O-ring is just filling void and making a seal but is mechanically limited against over compression. The old one was the same colour but smashed pretty much flat so pressure was getting past.
I got a "pneumatic tools" square drive kit off of Amazon to have a wide selection of potential square drive bits. Interesting to note that they had factory thread sealer on them so I put that back when I reinstalled.
The oil cooler o-rings where both cut though the top one was still sealing. I took the oil cooler lines out. It might not be the correct way but the plastic caps over the Jiffy-Tite were so brittle there'd be no way to get one of the push in style spreaders without destroying them anyway. I just pulled the covers off with a pick then pulled the clips out with a pick. After they they came loose with a wiggle. Easiest way to get them out of the engine bay is to disconnect the plastic joiner clips from both lines then pull them one at a time out the front after dropping the front air dam/splash guard. Get underneath and scoot them along so the rigid tube sections feed past the block and front axle assembly and don't get snagged. Take a 1 or 1 1/16in socket to get the fittings out of the block. Was so goo crusted that not sure which one was the correct one as the 1in didn't want to bite but the 1 1/16in felt loose. Plug with standard 3/8in pipe plugs. I got mine from Amazon in stainless, make sure to use thread sealer.