Have a question, on my 78 300D, the transmission was rebuilt in 2004....then it stopped starting so its been sitting since 2004...the transmission works fine but I notice hard shifting occasionally. I am getting ready to change the fluid/filter and was wondering if I should use the additive? I am thinking with fresh fluid it will help it after a few 100 miles, but then again the additive may help but it may also cause damage? I am up in the air.

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Fluid and filter will probably help. I've had good luck with Trans-X. It certainly won't hurt anything. I can't remember if the 78 trans is vac controlled or if it's all mechanical. If it's vac controlled you likely have a vac leak. If it's not vac controlled you'll have linkages on the passenger side running back to the trans, and adjusting those can change shift quality.

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