The Blue thing in the photo. Does someone have a spare? I am finding it surprisingly difficult to get one.
The photo isn’t loading. Are you referring to the interior gasket for the battery or the one that fits on the exterior around the housing (blue for HRM-TRI, yellow for HRM-PRO)?
I have some spare yellow exterior covers and probably some of the red gaskets that go inside somewhere as well.
There are usually a couple available on ebay at any given time.