Welp, I feel you should know that the TM G18C is more than capable of running black gas if you reinforce that front post with epoxy or buy the Guarder Nylon frame with the brass insert (around £25-30). You shouldn't have bought a steel outer - it will eat away at your slide too much.
I know hindsight is 20/20, but the TM Glock series have an inordinate number of upgrades available so if you end up sending your KWA/KSC (fyi, KWA is just the westernised arm of the KSC company) one back then look into a Guarder slide (the 7075 aluminium ones), an aluminium outer barrel (Guarder are good but there are plenty out there) and then a new recoil spring and guide along with that frame. All in all it's around £180 worth of parts - which is a lot but you won't get a Glock that looks nicer and still shoots like a TM.
Here's a good guide:
http://www.airsoftcanada.com/showthread.php?t=140496