There is a part in all Vanagon stick-shift transaxles called the 3-4 synchro hub—which has a flawed design. It cracks and eventually breaks without warning, usually before 150,000 miles, sometimes as early as 70K or 80K miles (see photo). This part transfers the torque supplied by the engine from the mainshaft of the transmission to either 3rd or 4th gear. Whenever you're in 3rd or 4th gear, this part is stressed. Sometimes only one section breaks (far left photo #1) and you might keep on trucking for a while with some weird shifting symptoms, giving you enough time to get to a shop and figure things out. But if two or three sections break simultaneously (photos #2 and #3, which is what usually happens), you’re screwed. Usually the transaxle jams in neutral, 3rd, or 4th. At any rate, when this happens you ain't going anywhere.
If you look closely at the photos, you will see that the cut-outs in the updated part (photo #5) are rounded instead of squared like the original design (#4). The sharp corner of the original design causes what is referred to in engineering design lingo as a "stress riser." Over time a crack begins at this sharp corner and begins to propagate around toward the next sharp corner, eventually causing that section to break off entirely. The VW-redesigned part (#5) to prevent this premature failure. If you are in the market for a rebuilt manual trans, make sure to ask the building if the ¾ hub has been replaced with a new one—even if the one that came out was the newer design—because those don’t last forever, either.