1. I found the service manual on line - don't know if the scan is still
there or not - you may wish to search - I also have a hard copy that I
insisted the dealer provide with my car when I bought it (new) - you will
want the real Porsche manual

2. Clark's Garage web site is very helpful, has excellent FAQs for many
common repairs

3. be sure to change brake fluid immediately to prevent further corrosion -
and use a pressure bleeder when bleeding the clutch slave or you will have
problems.

4. change timing belt unless you are positive of its age.  good idea to
change timing roller also.  I tension them by feel, never had a problem, but
there is a special $500 tool to help you do it right.

5. are you sure it's the core? there are some O rings near the core that
could be the problem.  Also, you can bypass heater for now, though if you
are in the great snowbelt, that may make driving less comfortable

6. Rennlist and Renntech is another good source for stuff and advice