A simple cheapskate thought ....
If your glass is foggy but is still holding the fluid in, simply take the top off once a year to check the fluid level and don't fix the glass ever.
Spending time and money to fix what isn't necessary -- isn't necessary.
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If it does leak, take the master cylinder off the bike, clean it well with brake parts cleaner and pour the inside of sight glass recess slam full of two part slow setting clear epoxy all the way out to the aluminum and let it set up well for 48 hours.
Once again, you now have a fogged sight glass that doesn't leak (at a total cost maybe $2 in epoxy) so now you take the top off once year to check it.
Big deal.
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The sight glass function is useless anyway -- proper set up after adding new pads is to fill the sucker up to the top so you can get maximum pad "out" wear movement backed up with reserve fluid in the reservoir. This fill point is up over the sight glass anyway.
And to check it, you generally take the top off anyway -- who is gonna trust the sight glass since it sees a completely different picture according to how the bike is on the side stand OR how the handle bars are tilted. Stop the leak, fill it up, and take the lid off once a year to check the fluid level.