stubbs_gt

180Pete,
Honestly your post causes me stress on the leaking head gasket, you have three contained systems,

Oilways, Could be leaking out or internally = medium risk leading to total failure if not backfilled with oil
Coolant, Could be leaking out or internally = high risk leading to total failure if not back filled with coolant
Combustion chamber, Could be leaking on combustion = bad and will get progressively worse

The combustion chamber leak could interfere with the emissions
The oil leak into combustion chamber could interfere with the emissions but you'd also get savage oil blow back if the engine is vent into the oil chambers
The coolant into the combustion chamber would definitely cause emissions failure but you'd see a pressurized coolant system and smoke from the exhaust.

The very knowledgeable people on here really need a bit more info to help you.

But a starting point would definitely be the head gasket