If the lock for your trunk or hatch does not lock/unlock with the central locking system when the lock is in the horizontal position, the mechanism is likely jammed. There is a little steel ball recessed into the lever that pivots in the plastic (difficult to see). This ball is what causes the lock to click into position when vertical. For some reason the ball can wear a groove into the slider plate and become jammed. When this happens, the lever that the central locking system uses requires much more force to move between the locked and unlocked positions. The vacuum plunger can't provide enough force to move it, but you may be able to move it by hand. Adding lubricants will usually not fix this problem.
You have two choices: either replace the lock (big $ from Audi) or just remove the ball and live without the little click telling you when the key is in the vertical position. To remove the ball, use a thin but sturdy knife between the plastic and the lever under the ball to pop it out. Safety glasses are a good idea here because that tiny ball will fly out. If this doesn't work, you may have to disassemble the lock to get the ball out. For detailed instructions on disassembling the lock, check out the Trunk Lock Fix on Chris Miller's 200Q20V web page. That info is for the type 44 cars, but our type 89 cars are probably very similar in this area.
