My 81 T-bird was purchased brand new in March of 1981 w/ 16 miles on the odometer.
Since then it's been a daily driver.
It used the cheapest dino 10W-40 up to last october, with Dex-III/Mercon in the AOD up till 2 years ago, with dino 80W-90 gear lube up till 2 years ago.
Now it uses 5W-30 w/ Mercon-V in the ATF, and Pennzoil PAO 75W-90 GL-5 gear lube.
It has 97,000 miles and is still a daily driver.
The engine is a 302 V8 with a Motorcraft 2150 2-bbl carb.
The engine was manufactured in 1979, so its about 22+ years old. I found some traces of sludging inside the engine and instead of a gunmetal/metal color, the inside of the engine is reddish/brown.
I've used ATF to clean out the engine twice, and it has helped with the front/rear main seal leakage. With 5W-30, it no longer leaks (not that I can see) and starts up easier in the colder winters.
I had to change the valve stem seals though, but other than that I think its in decent shape.
The 2000 Crown Vic I factory ordered is a different story. With today's materials, workmanship, and quality of parts I'd say it will last only 10-15 years TOPS.
As you can see I'm not one of those ppl that buy new cars every 4-6 years. I get one only when absolutely necessary.
If I had $25-30k to spend on a new car right this moment, I'd source out a late 60s to mid 70s muscle car and do a full performance restoration.
The reason being new cars are crap, there's more techno babble than substance. Maintenance is getting more expenisve with electronic sensor garbage, and the overall quality is bleh.