adding grease to a worn slip yoke

[old cool]

Last fall I replaced a rear u-joint. Upon removal of driveshaft, I noticed some leakage at trans tailshaft seal. There was also some slight pitting on slip yoke. The splines within the yoke did not appear to be mashed or worn enough to raise concern. I have driveline whirring (speed related) and a vibration between 30-35 mph. My questions are:

1.) would worn splines in a slip yoke (again, I didn't see anything that raised concern) lead to a vibration in floor shift handle, and steering wheel, at 30-35 mph?
2.) would worn splines contribute to whirring sound? I believe the yoke is a 1350 Spicer.
3.) Any risk to filling the spines with a heavy axle lube to see if it addresses whirring sound or vibration?

THANK FOR LOOKING AND HELP!

I'm going to start a diff thread on driveshaft phasing.