When I replaced my taillight bulbs I used LED bulbs, mostly because I had noticed that there was some heat damage on the bulb housing. I used the bulbs on this page; Super Bright LEDs - Miniature Wedge Base Bulbs
In the middle of the page you'll see a panel that says "T13 & 921 Miniature Wedge Base bulbs"
Click on the third thumbnail on the right. At this point you should see a photo with 921X12 written on it. The red version of that bulb is what I bought. I did a quick comparison in my garage by turning on the lights after I had replaced just one and the LED seemed a bit brighter and more red than the filament bulb.