I have a 60watt chinese laser tube that is about 1 year old, probably has about 400 hours on it or so

i have been getting poor reduced quailty cutting on thin plastics that i cut,

cooling is always good, mirrors are new and clean, and alignment is very good also

but i did notice that when removing my laser tube, where the laser comes out, on that back side of the glass or lens that covers the end of the tube there is some discoloration, i dont know if its the coating thats damaged or if there is gunk on the inside of the lens

Is there a way to attempt to clean this? there are two water ports right there at the end of the laser, and I wondered if i could use something like a pipe cleaner or such, just something that wouldnt scratch though, and fish it through those water line holes to get to the back side area of that end, they seem really close but i dont even know if that water path goes right up against that lens/glass cover or not, it looks like it may but there could be a gap for all i know.

has anyone had this or figured out a way to attempt cleaning it?

also, i know i have run mucky distilled water through here from time to time, so I am going to be sure to not let that happen anymore but I dont know if that is what has caused this or not, I dont want it to happen more or again obviously.

Please let me know if you have any ideas, It is cutting bad enough that if i can't find a way to clean it, i will probably have to replace the tube, but with such low hours, i would like to try and save this one.