If you crack open the headstock, the oil pump is visible in the bottom. It is a little bit of a pain to get to, but if I recall correctly there is a felt oil filter about the size of a half-dollar coin on the bottom of the pump that can get gradually plugged up. A piece of 1/8" felt from McMaster may be all you need to fix the problem. But I would suggest removing the oil line from the pump to the little distribution manifold and seeing what the oil ouput looks like there. The distribution manifold has small bijur flow/check valves that are known to get plugged over time. Don't mess with trying to clean them, just replace them. Monarch can supply replacements of the correct size, or you can find them elsewhere with a bit of searching.