It looks to me like it's made by the same company as my Underwood and someone else's Ambassador. That star on the bed and in the middle of that knob, and the crown above the name are the same. I'd say just keep cleaning deep, keep flushing the crap out and oiling it.
This machine was probably badged under several different names so you might have to look for a manual by picture instead of by name.
Cari