I don't know about the walker's mechanical concerns, but I do know from the experience of some associates, and my experience as well that the Turf Runner is the biggest piece of trash I have ever run accross as a "commercial" mower. I was told by multiple mechanics, and a Scag dealer that they were "f&*$ing garbage", and the dealer told me he never would have sold me one, which he did not, a salesman did.
They are a servicing nightmare, which includes hard to reach xerk points, gear boxes that need filled because they all leak...the experience of associates as well. The blades are stabilized by 2 10 mm bolts that shear off if you hit much of anything, like a mole hole. Then your blades will not engage anymore, just float around without spinning.
I could go on and on, but like was said before they quickly stopped making them in favor of the Couger which I hear is a better machine, but still far from a good machine.
Six years old is pretty risky with any mower, let alone this one. Oh yeah, and a mechanic told me that their is no machine worse to work on. What does that spell... big repair costs.
Think long and hard before you buy a Scag Turf Runner.
Jay