Trolling the threads leads me to an oft-times leakage occurring at the oil pressure light sending switch where it's metal body and the bakelite insulator are crimped over.
When I found leak diagnoses thread s indicating such I see that all the old guard members have weathered this problem.
It seems, that if a leak -did- develop and is just 'lived with', the oil can end up fouling the starter motor causing it's malfunction eventually. = expensive .
At about what point on the mileage clock do these sensor/switch become a problem?
Does the 'knock sensor' (close proximity) tend the fail, generally, the same way (oil leakage) ?

 

Mine failed, as identified by oil dripping on driveway, I replaced the sensor, don’t remember the mileage, around 120,000 miles.