1st gen, 350k miles, #3 cylinder misfires when cold...tried it all?

So, I've replaced the spark plug (all of them), coil pack (all of them) injector (all of them) and wires. The OBDII reader shows #3 cylinder misfire. When starting from cold you can feel the rough running for about 15 seconds, then it clears up and runs smoothly. If I clear the fault after it warms up It doesn't recur until the next day start after sitting all night. The plug had more build up than the others (I swap them at 25k, usually they are light brown, #3 appeared damp, and black. Every indication is that oil is leaking past the rings and soaking the plug, causing the rough cold start, then burning off when it warms. There's only a slight increase with oil burn (from not noticeable for the first 330k miles, to about 1/3 quart at 5000 miles oil change which also correlates. The only thing I haven't done is a compression check on the cylinders. Am I missing anything else? In the long run, I'm not really feeling up to a ring replacement in this engine.

 

Welcome to TW...you checked for a blown head gasket?

 

Which engine is it?

 

Do a compression check. You might have a burnt valve possibly.

 

compression check so many miles may need rebuild