This is about an LR3 2007 4.4L V8 gas 121K miles (Oct 2017)
One year ago I got the light engine with a piston 4 misfire on first 1000 revs. I took it to the workshop (USD500) and they couldn't figure it out. Then I had a misfire on piston 1 on first 1000 revs, then random misfire on pistons 1 and 4 and then misfire on all pistons together with slow O2 sensor response and catalytic converter below optimal operation. Then I got the head gasket blown out. I performed the test with the blue dye turning yellow, and combustion gases on the coolant, no white smoke on exhaust and no mayonnaise on the engine oil.

I'm considering: 1) trashing it out and buying a new car 2) change the engine 3) get the head gasket replaced.

For option 3): I'm concerned about the Instrument Cluster not showing the misfires, slow O2 sensor response and the message about the catalytic converter. So in this case I'm quite unsure whether spending USD6,000 on the head gasket job (Not sure whether the cylinder heads are cracked), might be actually the beginning of the O2 and catalytic nightmare.

Could it be that the O2 sensor and catalytic converter might be OK, but the heating was triggering error messages on them?

Can you advice what would you do? LR3 provided to be rather weak, but I don't want to trash the vehicle out.

What are the probabilities that after opening up the engine the heating cause is not found?

Is 10 years/121K the life term of these engines?

What is the probability that after a USD6,000 job, I would need to still be throwing so much money to be covering what seems to be weak design?

I estimated I spent USD15,000 in the last 6.5 years on maintenance and repairs, so i'm at crossroads.

Thank you for your advice.

Horacio