For the big money I just dropped into my W123, most of it was work that hadn't been done in 30 years and won't be needed again. The new suspension should last a very long time, the trans should go another 30 years, the timing chain will not be an annual service, etc.

It's not that the money is constantly being poured into it, but without the maintenance then it's guaranteed to be a lawn ornament.

There's a difference between driving a POS that needs work, and spending the money to fix it. We call it hood rich- owning high end cars but no means or desire to maintain them. So you see S500s and such sitting on bump stops because nobody fixes the accumulators. You hear a W123 clickety-clacketing down the street, but the person doesn't care to adjust the valves to quiet it down. Etc, etc.

I love the car. If I didn't, I wouldn't have dumped the money into it. Fortunately, I shouldn't have much to do besides regular maintenance and punch-list items for a while.