>I may have sort of fixed it by transmitting on AM mode in 1.8 mhz ham band at about 15 to 20 watts carrier by transmitting into a pure resistive 50 ohm >dummy load for about 20 mins each day for about 3 days.
Investigations into what causes the filter failures on the 897 and other radios point to moisture ingress due to poor potting, perhaps exacerbated by the dc bias on the filter accelerating corrosion. It has been shown that disassembly, drying out and cleaning of the filter elements will repair the filter (putting a new one in is easier!!!), so what may be happing in your case is that the heat from transmitting is drying out the filter,. You could try a hair dryer on the filter which may prove the point and be easier than leaving the radio on transmit.