You can replace the reed switch - they are cheap and easy to replace. It was a COMUS 2722 20-50. It is a slightly different size and higher sensitivity but works fine for me. Body length was 18.5mm, 2.6mm width.
If you are looking for a replacement rain bucket, you can use alternative brands -best are round ones, but there would be a ratio difference based on area. WD can accept a change I believe.