what preventative measures you would personally take, if any, to take engine into a long hopefully trouble free life.

EGR by-pass for a start (Yeah yeah, environment, etc etc etc. Don't care.)

I'm not sure that I would call that preventative maintenance in your example, I would class it more.as fixing something that isn't broken. For the cost of having that work done you might as well buy a slightly newer car. You've got to draw a line somewhere and take your chances with whatever you buy.

Personally, I wouldn't do glow plug / injector removal if it wasn't necessary to replace a faulty component. In a petrol car, removing / replacing the spark plugs could lead to stripped threads in the cylinder head (especially with current long service intervals between plug changes), which would be costly to remedy.

I believe the big issue with out-of-warranty ownership of a modern diesel with DPF etc is the longevity of the various pressure and temperature sensors that control DPF regeneration and emissions.

From experience with my previous Volvo V60, if one of these sensors should fail, it can take even a main dealer several attempts to properly diagnose the problem. I had a DPF pressure sensor fail, and it took three trips to the dealer and several days of workshop diangostic time for them to fix the fault.

I had an in-depth chat with the dealer service manager about this, and he told me (subsequently verified on a Volvo forum) that in the Volvo diagnostic system, there is no specific fault code for the DPF sensors. The fault code logged in the ECU relates to the EGR valve.

So the dealer replaced the entire EGR valve and pipework, only for the fault to pop up again. In the end, they had to resort to swapping sensors from a fault-free car one at a time, to identify which component was faulty.

Of course, my car was still under warranty, and I had a courtesy car, so it wasn't really a big problem for me. But if the car was out of warranty, I would have ended paying for several days of workshop time and replacement parts that were not needed before the problem was actually found and fixed.

So it concerns me that even a main dealer, with the proper factory diagnostic computer and software, cannot easily locate a fault. I've no idea if this issue is limited to Volvo, or if the lack of accurate fault codes applies to other marques too.

But based on that experience, I would only own an 3+ year old DPF-equipped diesel on condition of having a warranty that specifically covers the costs of replacing faulty DPF sensors.

There was I think a 'golden age' of diesels between about 1985 and 2005. They were quieter than before - well, a bit, and certainly quieter than the Perkins Prima or that wonderful 1950s two-stroke Commer lorry - and glowpug warming time had come down to a few seconds. And there weren't all the 3-letter acronyms which were installed allegedly for the sake of the environment but which tend to fail expensively at higher mileages.

SWMBO had two Peugeot 205 diesels - lovely cars which were livelier than the petrols (other than the GTI of course) and much easier to start when hot. She had a 206 too - generally a disappointment but the engine was the one good thing about it.

Yes, you save money in theory with a secondhand diesel - particularly if you avoid pasying more for it than you would have done for a petrol - but it's a gamble which I don't think I'd take.

August this year I had a dodgy glow plug on a Diesel Vauxhall Corsa and took it to the Vauxhall dealer, the mechanic that usually fixes and services my cars said I needed Vauxhall to get the correct codes as it was a 2010 tech2. The service manager at the VAuxhall dealer said that it would be £200 BUT if the glow plug is stuck and cant be removed easily it could get up to nearly £1,000 !!! the car had covered 120,000 miles, luckily the glow plug was fixed for just under £200..