Yes ,I have SEEN them too.I have one from 1980 that I keep from our old family home and it leaks a little with a somewhat rotted condenser coil no longer produced.
I brazed a charge port, pulled a vacuum and weighed in the correct charge,while charting temps and pressures for future topping off. To fully pressurize with nitrogen and try to fix a minute leak on an old unit MAY destroy it.Ask the guys who work on monitor top refrigerators.These window A/C's are just not worth it in MOST cases.Now please--It is my opinion only-thanks