I have 1985 300cd. Are there replacement parts for a auxiliary water pump, or do you just replace the whole unit?
Second, Where can I get a flex pipe that comes off the turbo?

AFAIK, There are no rebuild kits available but some people have rebuilt the pump using off the shelf o-rings and sealant. I recently replaced one on my 1986 300E, I bought it from Phil @ Fastlane for $100.