Warning thread hijack:
Conputer,
I have a 3/8" copper tube in a garden hose CFC, and have used it for literally 20 years. A couple years ago I began to suspect it was less efficient that when it was new. Now, I am pretty obsessive about sanitation, and always cold rinsed, then hot rinsed then sanitized the chiller after use, and sanitized before use. I thought it was as clean as could be. Wrong. For some reason I decided to run a test tube cleaning brush I had into it. I got it about 8 inches in before the curvature defeated me, but I couldn't believe the brown crap I got out of it. The efficiency went back to normal. I had protein coated the interior of the tube.
I straightened it out (that was fun) and ran a copper wire through it followed by a nylon string and a 45 caliber pistol cleaning brush. I couldn't believe the goo that came out. The thing was absolutely filthy. I was really lucky not to have gotten it infected.
Now I pump hot double strength beer line cleaner through it every three of four brews. The BLC is potassium hydroxide, and it will dissolve the protein/cold break that I think is being deposited on the walls of the chiller during use. The BLC solution always comes out green and ugly for the first couple minutes of pumping, then clears up. After that I hot rinse and starsan it to neutralize the hydroxide and sanitize it.
I don't know what configuration your chiller is, but I'll be if you do the strong BLC treatment you'll be surprized by the sh!t that comes out of it.
Just a thought for you to consider, even if the infection source isn't your CFC.