I went through this with a long-sitting (five years) 230SL with a 280 engine in it. Peter's suggestions are worth a try, but I think you should start looking for a used or rebuilt injection pump. We put hours and hours into trying to free up the injection pump but in the end the peanut butter residue of the fuel won out.

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Chuck Taylor
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