Just a water-cooled CG125 ... Tons guides in youtube & here for the air-cooled cousin...
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When barrel worn, CG150 (62mm) kit is a good alternative...
http://mydlm.taobao.com/category-1246973655.htm Search keyword "CG150" will show different brand had minor difference, choose the closest to stock config (ie. WYSIWYG)
http://www.mtctg.com/category.php?cid=5 also quite good to locate some oddball...