I have a 1994 964 with about 55,000 miles. It has been serviced by the local Porsche dealership since I bought the car in 1996. I rarely drive it these days, but when I do I am annoyed by how difficult it is to get into get. I have had the clutch replaced, and recently the rod that connects the shifter to the linkage dropped out due to a bad bushing (according to the dealership) and it had to be towed in. No way to shift it at all.

Now I find it is sometimes hard to get into first and second, third and fourth aren't too bad, but sometimes fifth gear is touchy too. On the other hand, sometimes it is very smooth. I can't really discern a rhythm to when it will operate smoothly and when it will shift rough.

Truthfully, I am suspicious of the opinions and service I have received at the Porsche dealer and hoping I might find some good advice on this forum. Thanks.

Define "rough" - too notchy, resistance moving the shifter into the gate, noisy, etc... each can have different causes...

If Porsche calls for useing SYNTHETIC gear oil and someone drained and filed with REGULAR gear oil that could be causing the hard shifting issue.
My advice to help avoid tranni issues: Do not speed shift, take a little extra time for RPM`s to go down between gears, then shift.
Then your tranni will outlast the engine IMO. Otherwise drive it like you stole it, the engine will seal better and leak less IMO. Letting the car sit for many months does not help engine seals. Too many people drive their Porsch like Grandma! Push it some times, the engine will actually hold up better in the long run.