Jeff Wisnia wrote:

Did/do they ever make ice cream scoops with a heat transfer medium
inside the handle to move the heat from your hand down to the blade,
or is what I'm feeling maybe just water which gets in past a leak at
the end plug when the scoop is run through the dishwasher.

Somewhere in the crevices of my mind I think I remember reading
something about sodium metal being used for things like that.

Can't say anything about the scoop, but sodium is solid at room temperature.
I've heard of it being used as a heat transfer fluid in a nuclear reactor,
but there it's hot and molten. And I don't know of any reactors that are
using that- I think all the ones I'm aware of are PWR.

A heat transfer fluid in any case would be useless here unless its density
increased as it got warmer. Don't know of anything that does that.

A quick Google gives this snippet
specific heat capacity of aluminium is 910 J kg -1 K -1 and that of water is
4,180 J kg -1 K -1

So a given mass of water can melt over four times as much ice cream as a
given mass of aluminium, assuming both start at the same room temperature.
This means a hollow scoop filled with water will work better as an ice cream
scoop than solid aluminium, since it will take longer for the scoop to cool
and hence it will be able to melt the surface of more loads to make them
easier to get out of the scoop. The water probably gets mixed pretty well
when you're moving the scoop about so you have the heat in the handle as
well. The heat from your hand well help a bit, but I don't know how much.
Unless the scoop feels uncomfortably cold in your hand it's not taking much
heat from your hand.