Hello Speedy611,
as far I know there is only Ming Cycle/Taiwan, who produces the official, genuine Strida - and no “variants”.
Sadly the magnet test tells nothing about thickness and structure of the used tubes…
I’ve had a further look at exactly the same bike, owned by a friend here in Vienna:
Generally, there are big technical differences to an original Strida, these SLO’s are simply not comparable (that’s meant without evaluation).
Therefore, I’m really sorry to say, some tips and tricks of our forum will not “fit”.
My personal tip is: Keep an eye on your frame - constantly.
Please be careful, human body repair is still difficult…
Does your frame also look like that below? 
(1024 x 768 here)
However,
there are different types of snubber’s, might this
explanation describe your type?
Please try the forum search (upper right corner) for “belt tension” (99 matches), “snubber” (76), “noise” (72);
the post titles are sometimes misleading, beware!
For the plastic: What do you think about “Cockpit” spray for cars?
(Just a guess, I’ve never tried something like that on my Stridas!)
Cheers from Vienna!
BSA