It sounds like the same basic set-up as my 300E. I don't know what the front of your engine looks like, so it is hard to judge the economies of replacing the pump as well. I don't know if the 350 pumps are trouble spots, so I guess I am not a great source of information.
I can recommend Silver Star Motors in Vienna, though, to do a good job at a fair price. Recently I have also had good experiences with Foreign Service in Tysons Corner.
I love ASC for their parts department - they have gone the extra mile for me more times than I can count. But I agree that their service prices are on the moon and there is no need to pay them unless you need their specialized diagnostics and it does not sound like you have a high tech problem!
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe