In the first link the literature describing the apron it appears that your apron has a built in oil pump. Monarch used this system on various models. That pump not only distributes oil to the apron but also the carriage and compound slide.
The pumps have a somewhat complex distribution system. The require service on older lathes due to clogged filter worn cam arms , stuck valves and clogged oil lines.
Rebuilding an apron prior to shutdown is a good step but the carriage oil lines may need servicing also.
This lathe is operating making parts . Be sure and manually oil the ways and parts like the leadscrews. Your feed clutches also get oiled from the internal pump.
You may soon have new wear issues without that pump system working.
Especially if its running daily
Oil everything good . Fill the reservoir in the apron to the sight glass line.
Google ; [ Monarch apron oiling.]
You will get hits about it on the Practical Machinist forum. Not necessariily on your model lathe but they used the system on many models.
I'm basing the internal pump information because in this link below it says that the [ apron is automatically oiled.]
Monarch Machine Tool Co. - Publication Reprints - Model "BB" 18" Helical-geared lathe | VintageMachinery.org
It could be a different system than I described above.
Information on your model is scarce.