Yes autozone sells it locally. No that wouldn't help the shifting, more vacuum to the tranny means softer shifts and if anything less pressure on the clutch.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k