I ride an early 90s Scott Unitrack CST with the original Shimano Deore drivetrain it came with. Same as this one. When pedaling, the right pedal has a peculiar feel like a sudden inward jerk at a certain position, roughly when the right crank is parallel to the down tube. This is more noticeable when pedaling lightly. Looking down when pedaling, the right crank appears to stretch or play inward and outward. There is no detectable play when forced with hands.
I'm given to think a busted ball bearing in the crankset is responsible, but I would like to get your opinion about the cause and urgency of the issue before I take it to the shop.