I've enjoyed the knowledge of you experts at radardetector.net forum, and finally I might have some tiny thing to give back to you guys.
The speaker on my SC55 died. It sounded crackly for a couple days, then it went silent.
I found this on part on Digikey, and it was very easy to solder it in.
You can find the speaker on Electronic Components Distributor | DigiKey Corp. | US Home Page, search Digikey part 458-1127-ND, or manufacturer part PSR-28N08A-JQ. $1.24 each.
Specs on this are 8 Ohm, 1/4 watt, 28mm diameter. I honestly just guessed that this was the correct part based on dimensions. I really wonder if it should actually be 1/2 watt--if I got that wrong then the speaker will probably fail in a few months. But its been running for a couple weeks now without a problem. I keep the volume on maximum which is probably why the original speaker failed after about a year.