So I just installed a PGC metal slide on my 18c after my original slide cracked. Was relatively simple and almost everything fit without modification.
I say almost everything fit because the rear 5ku night sight I purchased as part of a set didn't fit, upon further inspection it appears that the rear 18c sights are much different than the 17 sights so if you are going to order new sights make sure you order dedicated TM 18c sights!
On a semi related note does anyone know where extra selectors are available for purchase?