One easy place to begin is with the alternator. The brushes and voltage regulator can be easily inspected and changed.  This can even be done with the alternator remaining in the car - be sure to disconnect your battery first.

The main body of the alternator cannot easily be opened up though.

Here the brushes appear to be well along in their life but not requiring immediate attention, so I'll put those on my list and move on the next item. If you need to replace this part, then a replacement can be bought from Auto Parts Warehouse for about $20. You will need to enter your year and model but here is a specific ordering link for the 944 Turbo voltage regulator.

If you need to go deeper, insert a hex wrench into the and remove the main pulley nut (I held the pulley using a belt and used and impact wrench on the nut. You may need to use a vice or a hex wrench to keep the shaft from turning. Also remove the voltage regulator and the plastic insulator under the terminals.

Here are some photos & notes contributed by "Van"...

I [Van] had to separate the two case halves of the alternator. That was easy, but because the "electronics
plate" is wired to the back, there is a very limited range of motion. But I was able to
kind of tilt it back and away just enough to unscrew the 5 or 6 screws that hold it to the
back housing.

[Van] The pictures explain a lot of the disassembly, and I found my little slide hammer came in quite handy -- both to pull off the front retainer waster (which has a step on the back side, so it'll have to go back on correctly) and to remove the rear bearing.

While you have it apart, you may want to also check the diodes - this can be done with a simple multimeter.

The front bearing was a bit harder to remove, I was able to just budge it by tapping with a hammer and a large screw driver -- then I remembered a puller I once bought for a pitman arm on a steering box. That did the job as nice as could be!
 

The bearing sizes mentioned above are for a 944 turbo, they may be the same for the NA though. These can be bought from Pacific Northwest Bearing

Bearings
front 47mm od x 17mm id x 14 mm thick
rear 32mm od x 12 mm id x 10mm thick

Cleaned up and good for at least another 20,000 miles. One other note: once installed, the ducting adapter can be mounted to the back of the alternator. It originally had a open cell foam rubber strip seal - a material similar to the hood insulation pads. My seal was deteriorating to dust. I upgraded to a closed cell insulating strip; easy fix.  These little details are fun.