Funny, I check in to the forum and find the two latest problems I've had with my 300E. (See "Floating 300E".)
I'd check the fuel pump relay. Have your tech check the fuel pump itself to see if that is what caused your fuel pump relay to fail. If I remember correctly what my tech told me, if the voltage in and out of the pump isn't steady, it will stress the relay and cause it to fail, so replacing the relay turns out only to be a temporary fix.
My relay died on Halloween night with a carload of exhausted 6-year old princesses and one very miffed witch...
I was not the one in costume, by the way.
1986 300E - "Liesl"
1978 300D - "Gunther"