Is there any way to remove it and reseal it?
Obviously you'd have to dismantle the camera to get at it.
And it's likely you'd break it trying to remove it and take away the old sealant.
If so - a replacement or two is readily available if you do an eBay search for "watch glass flat" after you've measured the diameter.
And you'll need some epoxy resin or other strong glue for the re-seal.
And keep your fingers off the lens ...
Fiddly, but quite do-able.