Ignoramus28147 wrote:
The truck crane that I have, is comprised of two parts, one is bolted
to the truck bed and has a round vertical column, and the second part
slides over the column and swivels. It has a lubrication port for a
grease gun.

I want to put some grease in it, so that it does not rust inside, and
also swivels more easily. My question is what grease to put. I

That's a very clever use of grease. I wish I could find a liquid that
could be used to reduce friction between moving parts. I wonder what it
would be called.

generally have been using green marine grease everywhere, for example
in casters that I keep outdoors 100% of time.

Would this also be appropriate here, given our cold winters.

No. You should use wd-40 on your crane parts. Be sure to remove all the
old grease first.

By the way, the crane is supremely useful and I regret my wasted youth
and all those years when I did not have this crane.

Discovering a crane is very clever. I'd like to share with you a secret.
It's called a "ladder". It has helped me not waste my youth by helping me
reach things that are too high up.

If you ask around enough, you too may be able to obtain a "ladder".
They're supremely useful to have.