COMMUTER HAS VOR FLAGS APPEAR WHILE ON APCH; LEAVING HOLDING FOR CIRCLE TO LAND.

Narrative

WHILE HOLDING AT 10000 FT MSL AT OAB VOR; TRYING TO ESTABLISH COMS WITH THE FIELD WX OBSERVER; THE #2 NAV FLAG APPEARED AND DISAPPEARED ON THE FO'S HSI. AFTER RECEIVING LCL WX WE WERE CLRED FOR THE APCH AND SWITCHED TO THE UNICOM FREQ. WHILE DSNDING IN THE HOLDING PATTERN WE BROKE OUT UNDER THE CEILING AND SAW THE RWY. DURING THIS DSCNT THE #2 NAV FLAG BECAME MORE FREQUENTLY INTERMITTENT AND EVENTUALLY BECAME STEADILY IN VIEW. WHILE CIRCLING THE FIELD IN INCREASING RAINFALL; THE #1 NAV FLAG BEGAN APPEARING INTERMITTENTLY TO BECOME STEADY BY LNDG ROLLOUT. PRIOR TO THIS SERIES OF EVENTS THE #2 RADIO HAD A HISTORY OF BEING INTERMITTENT FOR SHORT PERIODS OF TIME (1 MIN OR SO). THERE WAS ALSO A HISTORY OF DUAL NAV FAILURES WHILE OPERATING THE ACFT IN RAIN OR SLEET OR OTHER VISIBLE MOISTURE. MY CONCERN WITH THIS SIT IS THAT WE DID NOT RPT OUR RADIO PROBS TO ATC. THE REASON BEING WAS THAT THE #2 NAV HAD JUST BEGUN TO BE INTERMITTENT BEFORE WE WENT TO UNICOM. WE ALSO HAD A FAIRLY HIGH COCKPIT WORKLOAD AT THE TIME. THE REG (91.187) STATES THAT A MALFUNCTION OF NAVIGATIONAL EQUIP OCCURRING INFLT SHALL BE RPTED 'AS SOON AS PRACTICAL.' IN THIS SIT IT DID NOT BECOME PRACTICAL UNTIL AFTER LNDG AND AT THIS POINT IT WAS NO LONGER AN ISSUE. I BELIEVE THAT WE HAD OTHER PRIORITIES. AFTER SHUTDOWN AN APPROPRIATE ENTRY WAS MADE IN THE ACFT LOGBOOK.