A lot about this post confuses me, but maybe its because I didn't see part one.
My simple answer is that testing is required to keep from buying parts. Looks like the dealer won't do it. This is where it gets difficult. This is sorta like Catch 22. The dealer has diagnostic test equipment but doesn't pay techs for using it. So they don't(This is established in warrantee work and becomes a way of life for dealer techs - in general - we obviously have at least one on this site that breaks all those rules). Independents seldom have all the necessary tooling and usually don't have the training = big problem.
This would all change if techs got paid what it was worth to do this kind of work. The only problem is that techs get paid what the market will bear. Thus it is very unlikely that your problem will get the necessary attention most of the time.
You are better off needing a waterpump, but then again you probably would DTY (do that yourself). The tech that does the waterpump will make a lot more than the tech that fixes this problem. That is the real problem!!!
Bosch Master, ASE Master, L1
33 years MB technician