I'd 1st suggest measuring the actual oil pressure with separate mechanical gauge - this can be plumbed into the engine via the current pressure switch port - if you use a Tee piece you can keep the pressure switch plumbed in as well and so see if the low pressure light corresponds to a low pressure reading.
As its intermittent and you have no rumbling or rattling noises from the engine its likely to be an electrical fault so 1st check the connection to the pressure switch is bright and clean and check back along the switch wiring for any signs of damage to the insulation
As if the wire is grounded out at any point then this will also turn on the light.
if this is all OK and the oil pressure is at least 1.3Bar ( 20psi) at hot idle then replace the switch
If you do have a low pressure reading and to turn on the light it will be very low about 5psi then replace the oil pump and ensure that the pump pickup in the sump hasn't come loose or is blocked
acks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine
1 bar is too low and a 1 way valve won't cause this
I'd ask them to check out the oil pump as the next step
a diagnostic may tell you if the pressure sensor was faulty but if the 1st pressure test was done with a reliable mechanical gauge then this has already eliminated that possibility
if you believe the measurement then the next steps are to remove the sump and remove the oil pump for inspection