What was found
AT FL390 ANTI-ICE SELECTED ON, STRONG DIRTY GYM SOCK ODOR FOR 15 MINUTES. OPENED LT AND RT ENGINE COWLS IAW AMM 71-11 FOR BOROSCOPE. NO LEAKS FOUND. R & R THE LT AND RT RECIRCULATION FAN FILTERS IAW AMM 21-25. COMPLIED WITH NO GO ODI CHECKLIST, NO FAULTS NOTED. COMPLIED WITH WC 3611-2010, REPLACED THE RT ENGINE HP VALVE AND REG IAW AMM 36-11, SYS CHECKED GOOD, NO ODOR NOTICED. INSPECTED 2.5 BLEED PORTS, OK FOR SERVICE IAW FIM 21-00-01/301.