Many of the E30 boxes that come off your donor car will have quite worn gear systems. Anything with over 100,000 on it I can highly recommend looking for play in the parts and then replacing the following:
Rubber boot
07 – RUBBER BOOT – 25111220912
Bush for the shifting arm
02 – BEARING SLEEVE, ROUND L=26MM – 25117519669
T piece parts
13 – GEARSHIFT ROD JOINT – 25117501309
17 – DOWEL PIN 23411466134
18 TENSION BUSH -25111203682
Plastic cup
06 BEARING, SHIFT LEVER – 25111220600
Clip to hold on to gear stick
12 CIRCLIP – 25111220379
I didn’t bother with the yellow plastic washers as many of the replacement stick – including the Z4 one I got don’t need them as the bit at the bottom is wider by the size of the bushes.
REALOEM page with these parts listed
Short shift the easy and less costly way – OEM BMW parts from other models!
You can use various different gear sticks from stock BMW models to create a short shift in your BMW Sportster. E30’s tended to have “Row Boat” gear changes from the factory. Our Sportster has a stick from the Z4 3.0 which is very short. A less aggressive one to use is from the Z3 1.9.
Here is a photo (from www.e30zone.co.uk) showing a comparison between various options:

Click me to enlarge
Part numbers for the gear sticks:
Z3 1.9 – 25117527252
Z3 2.8/3.0 – 25111222884
Z3M – 25117527254
Z4 3.0 – 25117543193
Z4 2.5 – 25117543192
PLEASE DOUBLE CHECK PART NUMBERS BEFORE ORDERING!
Here’s a picture it illustrate the the movement of the Z4 3.0ltr stick – if this is too short for you get the Z4 2.5 it’s a good compromise between the E30 row boat action and the very short Z4 one while still being nice a stubby at the top.

Here is the Z4 2.5ltr on Jason’s Sportster (the perspective it different from above, but it does move a bit further than the 3.0ltr one):
