What was found
(CAN) FRONT HEATER QUIT IN-FLIGHT AND RE-LIGHTED. FLIGHT CONTINUED WITH NO FURTHER PROBLEM. NEXT FLIGHT, HEATER DID NOT START. JANITROL TROUBLESHOOTING LED TO COMBUSTION MOTOR FAILURE - STARTED IF TAPPED UPON. INSIDE MOTOR FOUND ONE BRUSH COMPLETELY WORN. MOTOR WAS REPLACED ALMOST A YEAR AGO USING REPLACEMENT KIT NR 90E96-2 WHICH REPLACES ORIGINAL (NOW UNAVAILABLE) MOTOR P/N YZ14042. NOTED NEW MOTOR IS SMALLER IN DIAMETER AND LENGTH SO A KIT SUPPLIED ADAPTER IS NECESSARY. RECOMMENDATION: MOTOR SHOULD HAVE A BRUSH INSPECTION TIME LIMIT.