Like NJ300SDL said.
When it is hot disconnect the Vacuum Line at the Vacuum Shutoff on the Fuel Injection Pump and see if it starts. If it does start every time like that it is likely the Vacuum Switch on the Steering Colum Lock is not relieving the Vacuum right away like it is supposed to.
There is a rebuild it for your Fuel Supply/Lift Pump.
Newer Model Lift/Fuel Supply Pump Rebuild
Anyone ever replace the valves in the fuel lift pump? - PeachParts Mercedes ShopForum
606 Fuel/Lift Pump Rebuild
OM606 Fuel Pump Rebuild - PeachParts Mercedes ShopForum