1980 450SL fuel pump?
 

towards the end of a 45 min trip the car started sputtering and just in time to pull over to the side it completely shut off. Thinking the gas guage was wrong (reading about 1/4 tank left) I walked to a gas station and refilled with a gallon. The car fired back up but within a minute sputtered again to a stop. It will now restart if I leave it sitting for a while, but will only run for a couple of seconds until it cuts off again. Sometimes it won't even start up at all just turn over. I bought it about a year ago and have within the last 4 months replaced the air filter, fuel filter and distributer.

Any ideas what this might be? Just trying to get an estimate before I take it in somewhere.