Hi Jack. (Glad we are not in a US plane)
I don't know exactly what the differences are between different markets. That's the main reason why I'm here. To suck and learn. So I shouldn't really be answering you, but I couldn't resist the urge.
You see, I had a real seldom bird in my hands the other day. It was a 1989 300E with LHD bought new in Japan by a Norwegian, and taken home later. It's now owned by a surgeon, who likes it a lot. Could this be one of a kind?
Last weekend it just died on him, and he called for assistance. Normally I fix and send away as fast as possible. But this one called for full attention. A LHD Jap in Norway is cool. So I listened to the complaints and tales of joys and all that other normal MB stuff. I just knew I had to give this baby a personal full service, and the owner was thrilled.
I had it for 4 days, drove it a bit. Took the service, with new pads all around, new springs and shocks with shock mounts in the front. All fluids and filters, exept the transmission, as it was just done in december at the importer. New battery and voltage regulator, and I swapped some wires I know often fail.
But I never fully grasped how that CIS worked. It had the lambda, but missed a few sensors, had no EZL wheel, and a strange ECU. Well, I don't know if strange is the right word, but I suspect it had some differently configured EPROM's. In any case it had a very nice torque at the bottom, I would say probably the best I've ever felt in a ordinary sedan 300E. The system worked so perfect, I didn't dare to peek. You know. If it ain't broke, don't fix.
I had to weld just a wee bit of rust. I didn't charge any extra, I think when changing springs on older ones, one must clean and techtylize the upper spring mount. And it's wise to strengthen it with a rod. That's what I always do. For me and my friends.
If the Austrailan ones are equipped like the Japanese, and was fine with rust, I would buy it in a heartbeat. Look for rust, but I suspect dry conditions keep them nice and hole free. The engine is a real mile quencher, and if properly maintained, will never fail you. I have been hauling around many miles, snow and sunshine, with 260 and 300E, and in pretty rough conditions, and not had a single incident.
But you can't take the Toyota approach, just drive till it drops. Because if you do that to a Toyota, you'll come out with a small bill. If done to a W124, you'll bleed.
When testing, make sure the car is warmed up real good. During the test, take a brake for full 10 minutes, and see how it starts afterwards. If it starts well, it's a good indication of good injection health. And good injection health means good electric health.
If it doesn't jolt when you put the auto transmission in gear and when shifting, you can assume the drive train is sound. But it has to be fully warm to sneak out the bugs. And you have to be hard and demanding with the transmission. In the beginning, the bad stuff is felt at the extreme end only. And it isn't yours untill you buy it.
Good luck.
Regards
Geir