Tom, I went looking for such things. I had a hec of a time finding anything. You're best bet might be to contact Jobo in Germany or Omega-Satter here in the US. Although I have found them less than helpful on the Jobo.
The internal water bath heater has stopped working on my ATL-2300 and I've been told a replacement is 254.89 GBP ex VAT or nearly 400 USD. However, even considering the high cost I'd be reluctant to proceed without some form of diagram or documentation.