I used to be on the L188 Electra and had several in flight shutdowns.
There was no check list for loss of oil contents, but common sense should help.
On one occasion we were slowly losing oil contents from one engine so elected to shut it down in the cruise and re-start for approach.
On another occasion the Captain did not want to shut down until we had Reduction gearbox "Lo Oil Press" indication. This ended up with a shutdown as we turned finals. Not the best time to be doing this. Much better to shut down early and get set up for an engine out landing.