I assume you mean you are washing the band, not the monitor module? I have a polar H7 that has lasted me for years. I also just wet the electrodes with water as shown in the manual.
I do have to do a hard reset occasionally when the reading seem to get out of whack - Troubleshooting Polar H9 / H10 heart rate sensor | Polar USA
I also have an Garmin HRM Dual and it always seems to have a hard time connecting to apps on my phone. They both work, neither seem exceptional, but the HRM Dual does also provide Ant+ connectivity.