The stock Caterham OP gauge will only tell you that you have oil pressure, not how much. It is mostly decorative, so I did what MichaelD suggested and purchased an aftermarket mechanical gauge that fit. The peace of mind in knowing what the oil pressure actually is has been great. Also the occasional low pressure on turns has told me my oil level was low, so I was able to add oil and avoid catastrophe.
Chasing the sporadic no-start issue was my first great Caterham challenge, 10 years ago. Do what Skip suggests. The problem is, since it is intermittent, you can't reliably chase it down because it fixes itself while you are at it. After replacing my battery, starter, belts, solenoid, fuses, relays you name it, it turned out my problem was a loose ground wire. Since my Cat engine was pre-immobilizers, I was at least able to elimninate it from the cast of suspects.