99 Explorer firing issues, I think

[field]

I replaced with Bosch plugs 2 years ago and just now got my first engine check light. My OBEll shows #1 misfire but gives no code numbers. I'm guessing the newer OBElls show the fault in words now? I put the original spark plug back in #1 cylinder. Same #1 misfire reading occurs.

Slow coolant leak appears to come below cylinder #1 . Would any of those advertised additives seal a head gasket leak?

Or would Sea Foam help if it were an injector problem?

Thanks