arggg, another consumer sold on a $2k stainless liner
anyways... that Chimney is fantastic and deserves a stone cap or pure copper cap. Were those same caps present before the work you had done? if not then its most likely the caps, if those were the same caps then the person working up their used a flange or something of poor material (steel, iron, galv, etc.) in doing whatever he did (Im sure he built up cement to shed rain water and sometimes they use drip flanges, etc. in doing this. When you do replace the cap try to put some distance between the bottom of the cap and the top of the flu (10" +).
just to show you the simplicity of a stone cap here is a photo... There are a lot of folks here who give their right arm for a chimney like you have (me included!) and this is the proper way to cap it