It's really a hit and miss and when a part goes bad the results are very seldom identical. When a piston blows, does it always take out the high side? or when a tire blows out does it always send you for the ditch? Get my drift?
You have a stuck something somewhere, and I wouldn't be looking in the clutch basket first because it's the most work. A u-joint can break and it happens, it's not unheard of. For the time it takes, shine a flashlight into the driveshaft container and take a peek at the joint, it should be loose and movable, then move on from there. If the joint is tight, start your thinking from there. If the problem isn't at the joint and your discovery session at the basket doesn't show you anything, then you'll have to pull the engine and turn it upside down to open up the gearbox,, let's hope not,, and you would the first one to have such an issue,,, that I have heard of,,,,, not that I hear everything, I am getting older and my wife tells me I don't hear her mumblings so well anymore.
Keep us posted eh!