First - many thanks for the praise and the insightful post 
I mean each Strida user does promoting automatically - just by riding in public 
Regarding gearbox:
Your feelings sound very familiar to mine; it IS odd to hear something will work “forever” without maintaining.
Also I don’t feel really well if there is no detailed documentation (besides a few bad pdf pages and a patent in Chinese) available at the web.
(Actually I think there is no service manual existent for the KS3 - wished somebody would proove me wrong…)
I’m talking here about hard work - done very well it should look similar to this:
Schlumpf drives FAQ/webpage
Schlumpf speed drive workbench manual 16,9 Mb pdf file
Btw; the new competitor efneo told me they’re working on their manual.
It seems there is also no maintenance interval adviced…
Could it be really possible that nowadays are lubes on the market which can last “forever”?
I’m in doubt…
Regarding freewheel I do believe that the extremely different mileage experience could have been caused by just one reason:
Eventually were series of faulty freewheels manufactured (plausible could be for example anodizing mistakes) and spread all over the world.
Of course is this just speculation - please note - but that could explain the whole thing easily.
The freewheel is not cheap, that’s correct, but looking for possible alternatives you may return quickly:
gates-carbon-drive-cdx-freewheel-22T
Regarding Strida obsolescence - if you mean that in the sense of product maintenance and service - yes, you do have to worry.
If you meant that the brand could disappear (soon) then I’d say no.
Ming cycle is actually a bike supplying specialist and they do not hide that:
https://www.mingcycle.com.tw/en/
Ming cycle is, on one hand, pretty proud on “their” Strida and they use it as some kind of flagship.
But on the other hand is the folding bike segment too small to be important (enough), that explains their lack of interest in product service.
The lousy support has its roots in the fact that Ming has just bought a brand - but they don’t know exactly what that means because they are still mainly suppliers.
“Brand awareness” can’t be bought.
To give an example; imagine you are a car parts manufacturer.
Would you care if Chrysler, Mercedes, VW or Skoda does buy your products?
No, you would give a s… on who buys your parts - as long as you can sell them.
You also don’t have to advertise because the car manufacturers do that already, same with customer service.
Just today I found the following words, retweeted by Mark Sanders and obviously said by Will Butler-Adams (Brompton CEO)
“We haven’t created a brand - we’ve created a product and a service. Our customers create the brand”
Transferring above into Ming cycle mentality it must mean:
“We bought the brand, now it is ours”
Regarding spare parts collecting:
Good idea if you don’t like to wait for LBS orders.
The front rotors (140 mm) can be replaced by third party types, but the rear one (160 mm) has no bolt holes which is uncommon.
Also very unusual the belt snubber bearing btw!
I’m highly amazed that you didn’t notice that sooner - especially since you supplied more data.
This is for my meaning the absolutely typical “creaking rear hinge” behaviour.
To comprehend what happens exactly please watch this video,
https://www.youtube.com/watch?v=bdECyvRsizI
kindly supplied by our Hungarian collegue Zoltan - thanks again mate 
At about 0:20 running time note the sideways tilting of the front beltwheel which is caused by a rotation of the bottom tube around its axis.
This rotation transfers huge forces via the cup spring on the frame surface - the cupspring “bites” into the frame.
The next step is that the forces directions change and the cup spring “breaks loose” - that is the crack you hear.
The harder you pedal the more seizing cracks.
(A bit simplified.)
**Note: Before checking anything on the REAR end of the bottom tube:
Make sure that the FRONT end is tight - that means check both 274 bolts left and right of the locking latch AND look if upper an lower bearing are present/intact.
Surely not dangerous, but very annoying (at least for me) and the main chapter referring to product maintenance.
There ARE solutions and suggestions available - created by renowned persons like Mark Sanders or Bill Wilby.
Ming cycle DID receive above informations at least several times (partially personally overtaken at Eurobike Germany, including samples).
But the hinge remains the same. Period.
Considering that the brand exists over 30 years and I have only 8 years of Strida forensic studies to tell about - there is still hope…
However, please don’t worry about the rear hinge creaking, surely we can get rid of that if you want
Thanks to Mark (who sent me kindly his suggestions including drawings) I could manage to enhance my own solution massively.
Gladly I’ll share it asap, just for total reproducibility for everybody is some documentation explicitly required…and I can’t afford a secretary…