I posted this originally in the vintage section, but haven't been able to resolve the problem.
Basically - I decided to replace the pump myself, and with some encouragement/advice commenced the task in earnest..
There is one bolt that is concealed behind the harmonic balancer - and I can't get at it.
Everyone has said how easy it is to replace the part (http://www.peachparts.com/shopforum/vintage-mercedes/76618-123-water-pump-fitting-post491869.html#newpost
) - so I am wondering if I have misunderstood the process. Nobody mentioned removing the harmonic balancer.
Wondering if someone can confirm whether that's the issue.
Below is an image of the offending bolt - Other images of the problem are here: http://www.peachparts.com/shopforum/vintage-mercedes/76618-123-water-pump-fitting-post491861.html#newpost