This is a 400mw 405nm I got from o-like years ago, in the 1st pic you can see inside, my ac is on and there is some humidity today, also the diode is usually not exposed, it's sealed by O-rings on the front half with the lens that I took off to make the pic.
The 2nd pic is after I turned it on for a half a second, it was awash and overdriven, but notice how the unseen moisture on the can window was heated away.
I replaced the end with the lens and it works just fine, but I see why protecting the higher power diode windows would be more important.
Have you tried putting laser glasses between the camera to reduce the amount of IR when at near threshold? Maybe something with a low OD would attenuate enough while being clear enough to see the emitter?