Injector O-ring replacement - lubricant?

[Dave C.]

On a 1987 5KS (non-turbo)...

What type of lubricant should I use on the injector O-rings?

I've found references to both silicone and vaseline, but I'm not sure
either is the right thing to use.
Silicone?
I know silicone can damage the oxygen sensor so I hesitate to use it.
Maybe it's OK here cause it won't enter the intake?

Vaseline?

Maybe KY jelly?

Also, re: a piece of a plastic shroud that fell into the head ... I heard
one vote to just leave it there.  Anyone else care to comment on whether it
will cause damage?
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Dave C.