How much oil do I fill the headstock of a Harrison L5 with?

I have a recent aquirement of a Harrison L5 Mk2 lathe, I estimate made
between 1946-1947, its sat for some years and the headstock oil has
slowly leaked out (there is an obvious 'drip' on the drain bolt at the
back plus signs of weepage from the various shafts exiting). I
obviously need to replace with fresh oil but I have *no* idea how much
to put in.

I have a manual (that gives the oil spec[1]) but its for a slightly
later model which is fitted with an oil-filler and the instructions
are to ensure the level is right in the filler. As mine does not have
this filler the instructions are useless at best (and bloody annoying
at worst).

There are no sight glasses, no obvious markings, no bolts without a
purpose that could be for testing the level. While there are some
lines inside they appear to be just casting marks rather than for any
purpose.

The level is probably the same as the later L5 models and possibly
even the L5A/L6 so if anyone knows where they are filled to wrt the
spindle that would be helpful.

Anyone have any clues?

Druid

[1] And it is in comparison straight forward to get a 'new' oil to
replace what was specified 60 years ago.