After my range session yesterday I did a complete detail strip on my model 17. I saw that the spacer sleeve (part 31 on the schematic) was cracked. This particular firearm was heavily used when I purchased it and I've shot at least 5,000 rounds through it over the years. After I cleaned and reassembled it I shot a full mag of ammo through it and it still operated just fine. I will order a replacement ASAP.
Here is a pic of the broken part:
She will soon be 23 years old in September and has the Austrian proof marks.