Better shifting
 

Any oil brand recommendations for a 1984 915 transmission with only 91,000 miles on it? It's a bit difficult to shift.

You could try Swepco, but in reality, you'll probably need synchros.

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Be sure the bushings are in great condition and the linkage is adjusted properly. How worn is your clutch? These may be the true problem. FWIW, My transmission has about 163,000 miles and still shifts just fine.

I use SWEPCO 201 but I hear good things about Kendall as well. You DO NOT want to use a synthetic gear oil.

Motor and transmission mounts, shifter bushings, coupler,and clutch adjustment.

Kendall NS-MP

IMHO: If all the above are in good shape (particularly the shifter cup, bushings and coupler), the next step would be changing the transmission oil (I also like Kendall NS-MP). If those don't help, you have more serious issues with the transmission.

As others have said, I'd look into the shift coupler bushing, shift rod bushing and shift cup bushing and making sure the clutch is adjusted properly.

I'm a big fan of Swepco but I think you have bigger problems. Start with installing new bushing in the coupler and then an adjustment.

Do this before you do anything internal.

Richard Newton
Brake Rotors 101

I have an 83' 911 with 146k on it. I changed the shift coupler bushing a few months ago. It made a substantial improvement. It used to feel like I was shifting in peanut butter. Now it feels like I am shifting in butter.

I have used both Kendall Nsmp and Swepco 201 and prefer the Swepco. As stated above the external easy things like coupler, bushings and clutch adjustment should be checked and sorted. A clutch adjustment can make a surprising difference. Those things will likely get you farther than just a fluid change. However beyond that at 91k miles, your box may need internal attention soon. Mine was tired by 100k miles others have had better luck.

I am using now Swepco 203 90W. It contains Molly which was used by the factory.

If you don't know when the oil was changed, change it. Swepco is balky when cold. If you live where it gets cold, try Kendall. IIRC, Swepco is great for people who put a lot of power to the ground on a regular basis.