So you think this is due to low oil? I've read numerous of your old nitrous threads from the past 4 years and I'm considering spraying now. I'm hoping this is not the cause

 

Nitrous is definetly part of the problem. 75 instant HP is tough on the bearings and the wrist pins but my wrist pins seem fine. My compression is even and at a decent level for all 4 cyl. I always changed spark plugs. Always had her running on the rich side with the nitrous (used 100 octane for most spary crazy nights). But like any power adder (Turbo/Supercharger/Nitrous)
Bearings can be damaged. 75 HP IS THE LIMIT with Nitrous on the s2000. And your playing with danger...just like if you where running above 7 psi on a forced induction system with out beefing up the engine.....especially if the power comes on hard and fast (big hp gains in a small amout of rpm window range).

Althought I have not sprayed in the last 15 k or so miles.

What most likely happened at sometime the Nitrous was just to much of a bang and to much pressure. Probably cause some minor damage to the bearing. Over time that minor bearing damage became worse. Then a few times being low on oil
just speed up the process.

S2000 is a little cranky on the nitrous but still fun. Ya have to know that if you play your eventually gonna pay. A million things can go wrong. I sprayed alot...I mean ALOT!. I'm done with my nitrous phase...at least on the s2000. I have an LS-1 that loves Nitrous if I feel like playing around.