If you can't replace it with a newer plastic unit, they do make asbestos sealers that you can apply; they paint on. Most lumberyards and/or hardware stores sell it.

If it worries you change it for a plastic one. But you have already been told that undisturbed it is innocuous.

I have an asbestos water tank. The plumber said it was safe. He also said that its a much safer asbestos than the asbestos used years ago. But now, a year later I was in my loft and it looks like its been chiped or scraped. Its not broken or anything its not cracked but it looks chimped in a fewplaces