79 W123 300D Transmission

I can find no vacuum modulator adjustment on my 300D transmission, and am beginning to think that this must have a mechanical adjustment somewhere.
I am trying to adjust so that my transmission will shift into fourth
gear. Now it won't.
Also, I cannot get the kick-down solenoid out of it's receptacle. I have sprayed electrical anti-corrosive solvent onto the unit, in hopes of freeing it.
Any ideas would be appreciated.
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Not on the driver side? Round thing that may be red, green or black in color with a rubber cap in the middle? It is closer to the front 1/3 of the tranny... just above the transmission pan?
As for the kick down switch, pull the carpet out and follow the wire to the plug and just disconnect it.
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I'll look again--always a chance I missed something, as I did not have the car on the hoist.
I will disconnect the wire on the kick-down switch.
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