So I just noticed today in my 85 that when I shift I feel a vibration in the shifter. Most noticably during the 3-4 shift. While driving in gear seems fine. About 2-3 years ago I had new clutch, throw out bearing, and had to replace input shaft since the original was cracked.
Mine has a vibe in 3rd at high rpm's too...been like that for 3 years...but noticed it more after I put in my MGW. The stock shifter hides that vibe cause of the rubber in the shifter handle
Just had the same type of prob. It was the U-joints.
Id replace both ends, drain your tranny then re-fil it. Mine were so bad It was vibrating through the shafts of the trans. and grinding my throwout bearing into the clutch fork.