Both of my kraut wagens have lost tank vacuum. The 97 is OBD2 and its CEL lights up. The 95 is not and the car does not care. I don't know if the 96 T is OBD2 but if it is, it's required to test the EVAP for leaks by applying pressure, closing the vent and monitoring for pressure loss after 100 seconds. If your truck is OBD2 and there is no engine light, then the vacuum loss is very slow over time. (My 97 car is TLEV and this may cause it to be more picky.)

The only part of EVAP that is connected to manifold vacuum is the purge line. (Carbon box to valve at manifold)

The actual benefits of EVAP system are negligible but it is required to be working properly to pass some emissions inspections.

Like I said in the other thread I have not had to dig into this engine for troubleshooting but I think I would look at vacuum trouble as this can be inspected without touching the fuel lines and special equipment. You can just remove one of the hoses on the intake manifold and see if the idle changes. Vac leaks can come up in the strangest places, if you cannot find any leaking hoses, it could be a gasket somewhere on the engine (oil leaks are vacuum leaks too!)