Thanks for all the info/tips.

Is it really needed to install new cam chains? My S8 has close to 200,000 miles (321,868.8 km "google search"). I plan on keeping this car for awhile.

That's not an easy question to answer. I have never heard of the chains snapping but chains do wear and stretch over time. Personally, if I were spending the kind of money you are going to have to to replace the tensioners I would do the chains. This probably sounds obvious because that's exactly what I did.

If the extra work and time involved is a problem then I think I would take into account wether the chain slides had failed or not. Sometimes when the slides break up, the chain can end up running over the metal part of the tensioner grinding the tensioner away. If I saw any evidence of this, personally I would fit new chains.

At 200,000mls though, I would just do em.

When is your timing belt next due? Maybe you could do it all at the same time.

OK you convinced me to install new chains. I plan on doing the timing belt job at the same time.

Some reviews I've read about the special tool 3366 break while using it. Is this because of aftermarket version of the OEM tool? Or is it because of not using the tool correctly?

I would say because of not using the tool correctly - probably over-tightening it. The tensioner only compresses so far, and unless you've got a 200lb gorilla on the tools you can easily feel the change in torque on the screw as the tensioner bottoms out.

I've used the Laser Tools version and the cheap chinese ones and never had a problem.

This. It's the same tool as on a VW 1.8T. I've done the tensioner on a 1.8T a few times and the only time I ever broke one was because I wasn't paying enough attention and over-tightened it.

Ah, I had a feeling they broke because of improper use.