Reddit mentions of MettleAir MTC 1/4-N02 Push to Connect Straight Male Fitting, 1/4" OD, 1/4" NPT Thread (Pack of 10)

OK, so you have the older hobby type.It looks like the compression flange that holds the pipe in place is melted. The brass part is probably untouched, but I'd remove clean and reseat anyway. You'll need a new conmpression flange for the air assist pipe. I'd also order a whole new air supply line at the same time. I'd contact FSL via phone and order a new one. It may be the sort of thing that a hardware or even hobby store might have but I'd just go via FSL. While you're waiting, give that laser a good top to bottom clean. I mean everything. You can use windex and a clean rag for most of the inside, then use qtips and 70% isoproply on the mirrors and lenses. Don't use any weird cleaners like CLR etc. If something's really baked on, then use a bit of goo gone, but don't get it on the bearings - apply it directly to the rag not the laser. Check all the tube connecttions and try to clean everything. Don't worry about the barings, they're sealed so if there's shot or giving play (and it's not a case of tightening the wheels - see the online videos from FSL) then it better to replace them that try to lube them. Also chack that everything is squared an accurate such as the gantries and rails (you can measure between the top and bottom, left and right extremes). You may want to also buy new water hoses - my FSL 5th Gen came with silicone ones with split after a few years, so I replaced with clear PVC tubing (also better as you can see the water/bubbles in action so you know it's working).
Then when all the parts are replaced, do a full mirror and lens calibration (again see the vids from FSL).
Good luck and don't be afraid to post here if you need any help or tips -several of us, including the co-mod of the sub have FSL's.
EDIT: here's the sort fo thing you're looking for but again, get it from FSL as I have no idea about the thread size needed. Also, a lot of people suggest using pipe thread liquid instead of teflon tape when screwing the replacement in, as it apparently gives a much better seal.

https://www.amazon.com/MettleAir-MTC-Connect-Straight-Fitting/dp/B00S511S9I/ref=pd_sim_328_3?_encoding=UTF8&pd_rd_i=B00S511S9I&pd_rd_r=9T5ZKAP950Z9FMFWVD0J&pd_rd_w=CHJAz&pd_rd_wg=7tynf&psc=1&refRID=9T5ZKAP950Z9FMFWVD0J