I trust Rotella T over the Amsoil because the Amsoil might be 'gasoline car' oil with additives that'll make your clutch slip.
I'm pretty sure Rotella T will work fine in the TW as it's diesel oil (Used that stuff in my TDI VW.)
Given the prices on the jugs, I presume this stuff is over ten years old??
I'm running Rotella 15w40 in my TW and the clutch is fine. I use it because it's cheap and universal for all of my old air cooled motorcycles. I haven't had it not work in anything yet.
The worst that will happen is your clutch starts to slip and then you need to drain the oil and put something else in there to make it stop happening.
I like heavier weight oil in old machinery (or old fashioned machinery like this) which is why I'm using 15 weight.