This is a very common problem on the 602 and 603 diesel engines
If you discover either fuel or coolant leaks occuring right under the injector pump it is most likely a leaking fuel warmer (heater). Yes, that is correct. There is a small heat transfer component on the OM 602 and 603 engines that uses coolant to warm the fuel before it enters the injection pump.
Problem & Solution
Common among these chassis:
W124
W126
W140
W201
You should visually check this little heater on a regular basis. If they develop leaks it can come on suddenly and the leak can be significant. You have two options to repair it. Order a new part and install it. It is not difficult to do it yourself. If you live in a warmer climate you can remove it all together. Just connect the two coolant hoses together and run a new fuel hose to bypass the fuel heater.