I have included instructions to remove and re-install the fan clutch, Fan Clutch Tensioner and Belt, there are two motors from the 190E to distinguish the belt remove and replace instructions and belt route diagrams note that one is for a 6 groove pulley and one is for an 8 groove pulley, the belt route diagram and a diagram of the fan clutch in exploded view.
Again there is the difference in the belt removal and routing depending on the motor, so check the provided instructions and diagrams for the one that looks like your engine and check the Fan Belt Pulley for 6 or 8 grooves as that is the difference in the removal and routing. The two are denoted on the instructions and diagrams, so just note that when you look at them.
I do not know if it is an 8 mm bolt as I do not have that information.
If you can take the fan pulley and move it diagonally the water pump is most likely bad. Also, note in the instructions that other bearings in the solenoid, etc. Should be inspected as well. This is especially true in your case since the water pump bearing has play in it and that allows it to move out of center which will wear and damage other bearings that the shaft of the pump passes through as well as the clutch solenoid.
The instructions for one of the engines the remove a tensioner and belt requires a special holding tool. You can probably find something that will substitute for this at an Advance Auto or Auto Zone. They have a loaner tool program that provides some very specialized tools and test equipment. It only requires a deposit for the tool which is refunded upon return, so it is free. They may also advise a different tool to hold the pulley it all depends if they have a loaner that will work or not. Definitely look through the loaner tools as there should be a pulley removal kit or possibly a damper removal kit or some other equivalent that will work. They may try to get you to buy a pulley whip, but that only works if there is enough room to grab the pulley. This is if you have the 112 engine, so you may not have to deal with this as the other engine pulley comes off after the the fan is removed and 4 bolts which hold the pulley in place so the pulley does not require something to keep it from rotating if you have that engine. Refer to the 112 engine Fan and Fan Clutch Removal instructions to see the tool that keeps the pulley in place so the bolt can be removed. It is called a counterholder. Let me know if you need anything else.
Hopefully you have the engine that will not require a tool to hold the pulley from rotating. You may also find that stuffing rags in between the belt and a pulley may jam the pulley up enough to remove the bolt. You might also use a piece of wood, either should not damage anything but use your judgment, or you may find another way to hold the pulley once you inspect what you are going to deal with. I suggest doing this before you get into the job as identifying the engine you are working with and getting a tool to hold the pulley before you start will be easier than doing so in the middle of the job.
I you need anything else or have any questions, please let me know. I will get back with you ASAP.