So I dropped the car off Friday at a local independent mechanics' shop to carry out the 10-year major service (timing belt change, etc).
Around lunchtime they rang me up to say that after removing the old belt, they'd uncovered that the head gasket has failed and is allowing coolant to leak down the front of the engine. It wasn't wet (which would indicate a catastrophic leak) but there is clear evidence that seepage has been occurring behind the timing belt cover, originating from between the engine block and cylinder head.
I discussed the situation with the technician a bit who advised that it's not likely to worsen rapidly and I'll be able to have forewarning that it's getting bad by monitoring the coolant levels and watching for puddles under the car, etc. (I may be able to inspect for myself with the timing cover off also.) On that understanding that it may be okay for at least a little while I gave the go-ahead to proceed with installing the new parts and completing the service.
The tech advised that with a diesel, replacing the head gasket is not really viable as it's a very involved job, and that diesel engines are never really the same once it's put back together. ("Not a job we'd be happy to do.") He floated engine replacement (with a second-hand unit) as a safer option. Or promptly trading-in the car.
It bites, after the brouhaha with the transmission 5-6 years ago I was really hoping to get good service out of this vehicle for many years to come. It even felt markedly better driving back after the service (fresher, smoother, more responsive), but I can't escape this is probably terminal for the engine. The absolute best I can hope is the leak never worsens?
Pic below provided to me by the tech after removal of the old timing belt.
