[zombie5011]

I have been daily driving my 2008 STS since late 2011. Currently have 156k on the 3.6.

I had an ignition coil die at 90k, then again (same cylinder) at 148k. It does consume some oil, like a quart in between oil changes.
I replaced the passenger side motor mount due to vibration issues. I have the drivers side, just haven't found the time to get it in.
The alternator has been replaced, the power steering pump has been replaced, the water pump was replaced at like 45k miles due to a leak.

Inside the car I have replaced the blower motor twice, the blower motor resistor 3 times, the blend door actuator, and now it needs the other actuator replaced as I can hear it clicking and making noise. The driver side lumbar support stopped working. I opened it up and found the plastic gears were broken. I replaced them with ones I found at a junk yard and they lasted a couple weeks before breaking. Now it is disconnected.

I wouldn't consider anything I have done as major problems, just typical maintenance. I am actually in the market to get a full size SUV, but I can't justify spending the money because my STS still runs great!

 

[zombie5011]

Those plastic gears in the seat adjusters are so lame, it's like a very soft plastic/nylon which break way too easily. They aren't difficult to replace but metal would be far superior.
Motor mounts are a common replacement and I think they are supposed to much easier on the 3.6 vs the 4.6 but I still wouldn't trade it.
Blend doors become noisy after a while but mine aren't too bad, I don't use my climate control enough to be bothered by it anyhow.
Once the oil starts leaking into those spark plug wells it will eventually kill the coils, although there could certainly be other causes for it.

I actually 3D printed some new gears and got them to last a few days longer than the junk yard replacements. If I get bored, I will laser cut some out of steel and try them out.

The motor mounts weren't too bad. I got the passenger side out/in without any issues. The drivers side was a little bit more of a pain. Most of the online write ups I found (for 3.6 CTS) suggested removing the catalytic converters to free up space but those are also a pain to remove. I attempted to do it without removing it and was almost successful until I became frustrated and it was getting dark out so I just put it back together.

After I replaced the ignition coil for a second time, I went a head and did the spark plugs at the same time and did notice oil on one of the other plugs. It's probably time to change out the valve cover gaskets.