Okay. Who is he, and how do I find him?

Thanks for the replies. I think I'll just break down and find a new/used one. I'll keep my parts handy in case I have no alternative but to try to fix them. Any suggestions on where to find one? It's just the lock cylinder, so one off an old, rust-bucket junker would even do.

Thanks for replies. My problem is slightly different. Take a look at the "nipple" on the end of the plug. Don't confuse misuse of the term "cylinder" in the article The cylinder houses the plug. The key goes into the plug. A plug is alos often called a "core." It is best shown in Figure 5 in the bulletin here:

https://www.packardinfo.com/xoops/html/downloads/SC/SC-VOL29NO12.pdf

Anyway, the nipple broke off. It is part of the plug, and the plug and nipple are pot metal. If you understand the way the lock works, you can note that the nipple aligns inside a groove in the pawl. The pawl is defined and shown in the bulletin as Part F in Figure 1. A much better picture of it is also contained in Figure 3. The pawl is basically a rectangular piece that serves as the locking latch inside the cylinder.

Need to get that nipple back on or a good substitute....

EDIT: Thanks to Service Bulletins on this site, I got it. Now, the trick will be reattaching the broken, almost microscopic tailpiece back to the plug. These are pot metal pieces. I don't know if I will be so lucky. Any suggestions?

At the back of the plug (where the key goes in), a tiny cylindrical tailpiece is supposed to be attached. When the key turns, the plug turns, and the attached cylindrical tailpiece (which sits inside a groove in the locking bar) actually moves the locking bar to make it protrude so that you can't open the trunk when it is locked.