As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 1201 - DURING CRUISE, NR 4 PROPELLER RPM DECREASING BELOW 98 PERCENT, PRECAUTIONARY SHUT DOWN NR 4 ENGINE AND ACCOMPLISHED AIR TURN-BACK TO LIM. LANDED SAFELY. FOUND NR 4 PROPELLER VALVE HOUSING DEFECTIVE. REPLACED VALVE HOUSING PER MM, CHAPTER 61. OPS CHECKED GOOD MER MM, CHAPTER 71. (X)