If you're just missing the gate, that def sounds like a shifter alignment issue. Now that you know how to access the shifter retainer, the next thing I would do is take the shifter out and inspect it for breakage or excessive wear. Take the three small torx screws out that hold the shifter into the shifter housing and pull the whole shifter out.
If I recall, the '91 has the "plastic-ball" shifter. The upper pivot ball is actually a two piece ball with a large spring inside. The lower half of the upper ball extends down to the lower ball and is held to the shifter shaft with a retaining pin. check to see that nothing has broken. Sometimes the plastic piece breaks near the retaining pin.
If that checks out OK, then the other suspects are that the shifter housing (connected to the car floor) has come loose and is moving. In order to access the "special nuts" that hold it to the car you'd need to remove the center floor console. Those nuts would have to be tightened with a special wrench. You can make one by grinding down a 10mm socket (check the "SAAB tools" thread).
A couple other possibilities would be the shaft bushing at the front of the shifter housing is bad. I've seen them get destroyed by weld splatter on the shifter/transmission connecting shaft. To replace that bushing, you'd have to remove the whole shifter housing--big project if you're not handy. It could also be the bushing at the shift linkage where the shaft from the cabin meets the shaft on the transmission. That linkage is underhood near the firewall above the steering rack. I can't recall if the '91 has the newer "dogbone" style or the older cylindrical one.
