What was found
PILOT REPORTS AGAIN AT 23,000 FT, CABIN ALTITUDE CLIMBING. O2 MASKS DEPLOYED. PERFORMED EMERGENCY DESCENT INTO GRR. FERRIED BACK TO MKE. TROUBLESHOT SYSTEM. PERFORMED TWO TEST FLIGHTS. FOUND OUTFLOW CONTROL ROD NOT CLOSING VALVE IN FLIGHT BUT WORKING PROPERLY ON GROUND TESTS. CONTROL ROD END TOO TIGHT AT AFT END. LOOSENED ROD END BOLT. OPS CHECK GOOD. RETURNED A/C TO SERVICE.