I’m in agreement with cigroller about the oil pressure sender. These things are cheap anyway so you could stick one in and if the light still comes on then you need to start worrying.
The old Subarus were prone to oil pressure sending unit leaks. Some age and generally after a cold winter the plastic would start cracking or deforming which would then lead to leaks and/or the oil light flashing on.
Some of the older Fords were also a bit prone to this.