You didn't say if there were any problems prompting this recommendation. If you are having idle problems like surging or stumbling, or a failed emissions test, then looking for vacuum leaks and replacing the injector seals and air hoses makes sense. Otherwise, count your blessings and save your money.
I say this from personal experience. I just finished re-sealing the intake manifold on my 380 on an indie's advice and about all I can say is that it was a lot of work for no benefit.
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