Dear wise-folk, turntable motor grinding after oiling?

This is a 40 year old turntable, a high quality belt drive Pioneer PL-41. After dropping a couple drops of 3in1 oil into the motor lubrication point (the manual says to lube it regularly), the motor developed a quiet grinding sound.  It took five hours of play over a month before I noticed it with my ear next to the platter.

Did I stir up some gunk in the motor?  Thanks in advance for any suggestions!  You are so helpful!

PS This sounds like a pinch of sand is in the motor, but the grinding/crunching sound is quiet.