Now this is interesting:
http://www.enginehistory.org/Wright/R-2600/R-2600CaseHx.shtml
"Cylinder Rust and Corrosion
The most vexing problem was rust and corrosion in the cylinders. The Corrosion
Committee, established by CTI-1325 (May 17, 1943) wrote, "We do not know the answer but
are beginning to suspect Gremlins." The FBI checked for sabotage. The "epidemic" of
December 1942 to March 1943 was corrosion, and that of June-July 1943, rust.
............
I seem to recall the same thing happening to Packard Merlin engines made in the USA, this occurred for a short period and the same causes (ungloved hands, added to it were other assemblers eating salted peanuts for lunch and not washing their hands afterward before gloving up) were found to be the culprit. My source for this was my aunt's friend - now long deceased - who was one of the engineers assigned the task of converting the Merlin for use in P-51s. One of my life's greatest regrets was never getting his story down in detail.