I have been driving my 1983 300SD for 14 years, owned it for 17 years. Three of those were with my mum.

I remain satisfied that this is not only one of the best cars ever made, it is a superb value on today's used market, if you do your own work. I prefer the W126 S Class to the W123, as you get more luxury for your dollar, though some might argue that all those seat motors etc. are another thing to go wrong. That is not my experience. I also have a strong preference for the aesthetics of the W126 over all the other big Mercedes sedans, but that's just my opinion.

A quick perusal of Autotrader.com for 1983-1985 300 SD cars discloses 37 US listings between $2,500 and $5,000, with mileages of 150,000-300,000, where disclosed. Stated differently, these cars are abundantly available and cheap.

If you can handle a diesel's leisurely acceleration, can live without air bags and ABS, and are willing to catch up on the deferred maintenance that many second and third owner cars suffer from, here are the economics.

You need a pre-purchase inspection - the mechanic checks compression and the transmission, you check all the accoutrements, not least the body (body work is expensive) and the interior (leather is also expensive). My inclination is to try to get a car with no more than 200,000 miles on it, giving you a good chance of another 150,000 before top end work is called for. Focus on one with all service records, with an emphasis on regular fluid changes. $200 for a thorough PPI.

When the 300SD returned to me three months ago, it had only had basic oil changes performed. Diesels are not low maintenance cars if they are to run properly. Their best (and worst) feature is that they will run horribly out of tune, but the goal is to have a car that runs perfectly. Mine, then, was a victim of deferred maintenance. Fluid leaks were abundant, rubber was shot and the transmission shifted horribly. Here's what I had to do to make it perfect, with parts costs estimated:

Start with a maintenance service - filters and fluids $150.

Worn discs dictated a brake job, $70 for the discs and $40 for pads.

A rough idle can be cured by new engine mounts , call it $30, and a good injector overhaul followed by Diesel Purge. That lot adds $15.

The oft neglected sliding roof costs pennies for the grease.

A suspect charging system is frequently fixed with nothing more than a new alternator regulator for all of $25.

Fix that broken window for all of $2 and some labor.

A bad fuel sender replacement is expensive at $80, but essential, as is a new tachometer amplifier at $70, the latter nice to have.

If the timing chain is stretched much over 7 degrees, replace it or risk a top end rebuild. Nice to have this checked at the PPI - the illustrations are for a V8, the I5 is even easier to do. $150 in parts for the chain and tensioner.

The bypass hoses probably leak, and that's an easy fix for $30 or less.

There's a good chance the cruise control is faulty - a $150 fix.

A leaking differential is an easy fix, if messy, costing some $5 in RTV silicone and $7 in gear oil.

While you are at it, do a transmission service as it's probably way overdue, then follow up with a thorough transmission tuning and make it shift like it did when it left Stuttgart 20 years ago. $35 for the filter kit, $15 for the ATF.

Finally, if your shifter goes click-click, replace the shift linkage bushing and things will feel right - $3.

While you are spending wildly, $15 or so will replace those sway bar links.

Now you get to the cosmetic stuff.

Some cracks and discoloration in the seats are fine, fix them with ColorPlus poducts available in the tint to match the originals - $200 if you go crazy and redo the whole interior. Major tears and dog marks are not fine - find another car.

Leaking seals must be replaced immediately, or you will get rot. A tricky job - reckon on $80 for a door, $40 for the trunk, and don't sniff the glue.

Now that you are almost done, and given that you share my insanity, do your baby a favor and add keyless entry, keeping costs down to $125 by learning from my mistakes. That is, of course, a needless luxury, but you owe it to the car and yourself.

Oh! but all those special tools I will need, you say. Well, the bent valve wrenches can be made at home or bought for $60, the crowsfoot injection line and deep 27mm socket add another $100, a vacuum gauge for the tranny work $35, an Eezibleed for the brakes $40. Tools that will outlast the car.

Let's see. That lot adds up to some $1,500 on top of the cost of your car. Then, enjoy the lower vehicle license fees the state will charge you and drive the best car in the world for another 150,000 miles. But most importantly, enjoy your ride in the Best Car in the World. Just remember to keep the maintenance up.

And, if you are really good, take pictures of all of this as you do it so you will remember how to do it next time....