Recent posting on "the other side " entitled --How to do a water pump - 1 Hour on W202 C180 a comprehensive HOW TO post with photos for anyone wanting to try it as a DIY - you will have to register to see it.
Just fitted 1 to mine, 1 hour's pushing it a bit ! More like 2 if you rush, or maybe i was just too consciencious in cleanliness/perfection. I used a chain type filter wrench to help hold the w/pump pulley & made/modified a spanner to fit the large (38mm?) nut on the viscous.Not an easy job because you need quite an array of spanners to fit the awkwardly placed pump bolts, but yes,diy-able.