94 B18b transmission. I have it off the block and want to perhaps fix a little problem i have but i dont want to order wrong part, so here is whats going on, you tell me what you think it is.

The problem is centered around 4th gear:
if im in third and go into 4th either quickly/ or high RPM's it grinds a little, same applies if im in fith and drop quickly into 4th it grinds. Does that sound like synchro or gear, i was leaning more towards synchro, what do you think??