Which O-ring goes on an LS oil pickup tube, and how do I install it without pinching it?

Use the O-ring made for your pickup (aftermarket pickups include one, like GM's). The key is installation:

• Lubricate it generously with oil before pushing the pickup into the block. Speedway warns a dry O-ring tends to tear, and a torn O-ring causes oil pressure problems.

We don't have a GM part number for the O-ring as a source, so match it to your pickup.