I have run a w124 e300d on fuel mix same as yours with ten percent petrol added for over four years and then progressed to a w210 turbo diesel starting on biodiesel and eventually going to veg .
I had similar trouble with my w124 , filters plugging up etc after about a year and a half on wvo mixes.
What happens is the fuel tank gets a lining of grease /a sort of semi solid grease build up in it , take fuel cap off and scrape a finger around inside the tank neck ... the junk that you scrape off will melt if heat is applied to it .
Now what happens is once this build up gets bad then adding a heater in the fuel system melts it and it flows around the system with the fuel and eventually builds up in filters and blocks them.
So you need to remove the fuel tank and clean it out , I did mine with hot water /caustic soda mix and when refitting I did away with the mesh on the in tank filter .
Its possible just removing in tank filter mesh and cleaning or cutting it off its base will sort the problem out.
Reversing fuel lines over, swap inlet and return over on the under bonnet / hood connetions ie where rubber hoses join under car steel lines, The return line feeds back on the saloon anyway to a plastic bell shaped device that covers the in tank filter , so if the in tank mesh is plugged and cannot have fuel sucked through the reversing lines lets fuel blow through the gunk to return .
But I am confident the tank just needs a good clean out , or fit another tank or can somewhere and run it from that.