After following a thread in this forum on 'reviving' the intensity of my HUD, I cracked the glass. Did the following to prevent more breakage. No biggy because it still works.
A hint after-the-fact....when removing the glass to clean the mirror beneath use a hair dryer on lowest setting to loosen the adhesive under the glass. This should allow the glass to be removed without cracking IF you pry VERY gently while heating!
I can now see my HUD in the daytime! Amazing how dirty that mirror can get!