According to some resources, the pickle fork is not a part of the C-check, since it is a lifetime part that would endure 90000 cycles+.
The first time they found it was apparently during a rebuild of a 737NG to a freighter.
The replacement part(s) for the pickle fork is made of titanium instead of aluminum.
But now they found new problems :
Aviation Week is reporting that cracks have been found in other locations on the Pickle Forks and planes will have to be re-inspected. This is behind a paywall.
https://aviationweek.com/commercial-aviation/new-issue-prompts-expansion-737-pickle-fork-checks?utm_rid=CPEN1000000897724&utm_campaign=22066&utm_medium=email&elq2=6e60e0bad2bd4ef98846799387403cd1 Fair use extract:
"Checks of frame fittings and failsafe straps, or pickle forks, turned up cracks in four aircraft near fasteners that were not covered in the original inspection order issued Oct 3. As a result, Boeing on Nov. 5 recommended that operators expand the checks to include eight fasteners, up from two in the previous order. FAA will mandate the checks in an airworthiness directive (AD) slated to be published Nov. 13 and effective immediately."
"The new directive, which is expected to be adopted by other regulators, calls for aircraft in the high-cycle category to be re-inspected within 60 days. Aircraft in the lower cycle category must re-inspect the entire area within 1,000 cycles."
According to a friend of mine who flew 737 until last year told me 2 old SAS 737 will be scrapped instead of repairing their pickle forks.
All airplanes crack - that's why they have inspections which I detailed in a post about 10 pages ago.
I suspect they weren't grounded... I suspect they were pulled out of service for a scheduled C or D check; but given Boeing's evil boogey-man status, a reporter told the story as if they were grounded by some overseeing authority.