Most likely, oil from the interior of the IP was able to be suctioned past the failed diaphragm on the shutoff valve on the IP,
and down the vacuum hard line into the cabin where it pooled in the vacuum switch on the steering column lock.

The oily residue in the vacuum switch is creating a seal that the internal spring of the vacuum switch cannot overcome when the key is removed from the ignition.
Hence the inabilty to start the engine, until you release the vacuum.

You need to remove and clean out the oil from the vacuum switch on the steering lock.
The vacuum hard lines shoud be cleaned out as well.
The rubber vacuum connecters to the vacuum switch are probably oil soaked, and should be replaced.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022