Funny you mention a 951 that is the exact car I am working on right now (an 86). Certainly Rennlist has been not very helpful, but I think its just in the nature of the internet to have an extremely bad signal to noise ratio. I use the term experts lightly but I find that the knowlede online goes way beyond what you can find in the service manual. Roughly 75% of the time I can find an answer and the rest I need to do some basic science or logic like bench testing a turbo.