I would say his mechanic has done this,as quicky patch up. but it's far easier to repair the system properly!.
Your VIN is a 500 SEC.so it should have the electronic idle control.
Do you have the diagrams for the vacuum lines to WUR?.It's pretty important that it's connected in the correct fashion because warm up ,aceleration and general running depend on it. All of the WUR's are stamped made in france. The last three numbers of the part number should be 101. it must also have two lower connections and one large top connection.
I see from your pic that the plug leads are looking old, if you have access to a multimeter,check the resistance from cap to plug end. They are very sensitive to correct plugs and good leads.Another reason your car will be hard to start when hot.
You also have the rubber cover over the distributor cap. LOSE IT! Mercedes don't even list that as a part anymore because of the problems it causes.
Everything from moisture getting trapped under it,to dirt causing static electricity causing spark leakage.