Bob Engelhardt fired this volley in
:

I'm inclined to try gear oil, but I thought I'd collect RCM thoughts on
it first.

I'd more naturally assume that _either_ they were made of oilite to begin
with, and the grooves were just for maintenance oiling, where the oil is
expected to run out after having created a film, OR that they were
intended to be greased.

When such a sleeve is intended to be oiled instead of greased, there's
usually a felt washer on the ends or a wick in the oil hole to soak up
and re-feed oil into the gap as necessary.

LLoyd