I think its been discussed here several times about the 3 window headstocks suddenly dropping oil level in the front bearing window, or slowly leaking down. My 1951 MfG model EE, does it all, it can hold the oil level for months, suddenly drop oil level, and slowly leak it. It always ends up in the center compartment.
On the single window headstock, the spindle bearings oil from the trough at the top, oil gets to the trough by climbing up the small gears that drive the alternator that powers the tachometer-"the later tachometer shows rpm with the machine in reverse" the trough has a sharp edge, that scrapes the oil off the side of tachometer drive gear. Amazingly simple, no pump, and depending on some adjustments can provide too much oil. The basic adjustment is using a feeler gage to determine the gap between the gear and the trough, "closer would provide more oil".
When the spindle is reversed on the "one oil window headstock" machines, the tachometer gears pick up more oil then when in forward. I am mentioning this because if the machine has sat for some time, it is beneficial to warm up the machine by running it in reverse at around 300 rpm for a few minutes, this will flood the oil trough, and get some oil to the end gear train, if you want to cut some threads right off. Also, during warm up, place the gear box in coarse feed, that will kick the oil around in there.
And, after all that nonsense, back on the topic, because the single window headstock machines pick up more oil in reverse, if they are not ran forward again, a little oil may leak out the front of the spindle cap....