I have to say this - there are several write ups on how to bypass the center console fader switch. Its really easy. It took me 5 minutes.

The oil is coming from oil in the vac system that is draining oil- a P.O. may have let a vac issue go to long and some oil was sucked into the system is now draining out of the climate control switches. You want to check the vac system for leaks and the climate control behind the panel for a leaky vac hoes. You can disconnect it and drain it but 1st make sure the vac system doesn't leak.

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1984 300D