I have only burned through 1 x M140 and 1 x NUBM44 can window, and I have over a dozen happy diodes right now, but I don't take the lenses in and out except during the build or if I need to replace a cracked 3 element, I know we are much safer with the ( can & window ) than without it.
I mentioned it in the 44 thread that I like to use a 3 ele with a 3X BE and also a G2 with a 6X cylindrical pair and then a BE or not, but either way the diode is protected as the BE gets all the adjusting and the diode's primary lens (3E or G2 ) stays fixed where I set it usually between 20 and 100 feet with 100 and infinity being about the same.
It's really easy to use a 3 element and a 3X BE and you get a longer working range as well as a protected diode window, but I have not gone this route out of necessity.
If you are really concerned you can order your diode pressed into a module by DTR with a lens of your choice ( G2 or 3E ) already installed then you can simply leave your G2 or 3E lens in place and focus as needed without removing the lens unnecessarily.
Now in the case of GBall diodes I have used the NUBM06 with GBall lens intact followed by a 3X BE with good results, it just depends on the GBall lens RX, they vary from block to block as the OEM requires.
astralist can you see this pic and the emitter? If so it could be a word that's causing it to be blocked.