Sounds good in theory, but one hole.. if it is the engine mount, it would be RPM Dependent, so the vibration would be at the same RPM regardless of what gear you're in (IE: you'd feel it four different times through your shift pattern)
Possibly your OD is chattering/hunting? does it go away when you lock out OD? Just a thought.
PS, if a needlebearing seizes in your U-joint, you won't feel any excessive play in your shaft. the only way to tell is to spin the cap (PITA to get out of the yoke though)
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