By design E30 shifters are doomed to go sloppy over time because the materials that keep it tight are made out of things like rubber and hard plastic.
Here is the no-bullshit way of getting that shifter tight again.
You will need parts 6 and 13 from the dealer. Part 2 from a third party, and possibly a new shift lever only if the inner bushing is worn out (mine was in great shape even though the rod joint was worn to all hell).
Number 13 is part number 25 11 7 503 525, do NOT get the aftermarket MTC unit, it is build like crap, the holes do not line up for the pin and the horizontal tube portion is welded slightly off axis. This joint changed in 8/89 to be symmetrical, the asymmetrical pre 89 version is still available (although different part number), however you will need the newer version if you are following my steps. Both joints are completely interchangeable on our transmissions. If you are using OEM selector rods then you must match the same time period rod with the same time period joint. We will be changing the rod so you will need the newer style joint.
Number 6 is part number 25 11 1 220 600, this part can be ordered from third parties (make sure its brand name SKF), or from the dealer.
The next thing you will need will be a dual sheer selector rod or they are also called DTM style selector rod (DSSR for short). It will replace part 10 on the diagram. These units are roughly $120-130 dollars but they make all the difference. Essentially the DSSR grips both the shifter and the joint from both sides, not allowing for the side to side play that is allowed by the OEM design. The OEM design only grips the shifter and the joint from one side and thus not only is it sloppy to begin with but it also wears away the plastic bushings inside the joint and shifter over time.
I recommend getting a DSSR from a supplier who does not require the use of bushings at the mounting points. Some companies require the reuse of the yellow spacers that go on either side of the mounting pins. This is completely unnecessary and those bushings will wear over time, it is best to have no bushings and a very tight fit so it never wears out.
As you can see here stock only holds from one side:
The last thing you will need will be derlin bushings that will replace the rubber bushings on your shifter carrier (#2 on the diagram). The OEM design uses a rubber insert that flexes under load, this is solved by using derlin that has virtually no give.
This combination has produced this result for me: