Dear community,
insensitive pitchbend seems to be a problem many OP-Z users came across.
I can now say that it is replaceable and quite easy and fast to fix.
BUT: You will have to order a replacement part directly from TE. Which hasn’t been a problem for me at all. I contacted support on Sunday evening, they replied on Monday morning and I got my replacement via UPS today (Thursday). It is NOT a part that you can order via iFixit, it’s shipped directly by TE.
You will have to ask for the following part “OP-Z pitchbend + microphone”:
They will then send you a shop link with a pre-filled cart, containing the part. It’s just the usual TE shop. No, I can’t share the link, the cart is only usable once. You can order more than one part.
The price was 20€ for me. I don’t know what it would be in $. I don’t know if you can get it for free while warranty lasts. Could be possible. You have to decide for yourself if it’s worth it for you.
As you can see, the part is a small flexcable that is attached to the bottom left of OP-Z’s inner frame:
To open the OP-Z you will as usual need a Torx T4 screwdriver.
The flex cable is self-adhesive. The old cable can be easily removed/pulled off. It didn’t leave any glue on the frame so I could immediately replace it with ne new cable. (Dis-)connecting the cable from/to the main board can be a bit fiddly but it isn’t sorcery.
Placing the new cable on the frame was really easy. The frame has some pins, the cable has some holes, you can’t do anything wrong.
After reassembling the OP-Z, pitchbend worked like a charm.
I guess it will never be ultra sensitive, you still need more pressure than I’d wish but it works. The whole project took me around 15 minutes. You can watch this YouTube-Video (not mine!) for better instructions:
(The video states you remove Torx T5 screws but they are - as I mentioned - Torx T4. Don’t get confused by that.)
I hope my post is of any help. All I wanted to say:
Don’t hesitate to try for yourself, fixing the pitchbend is possible and EASY! (But it doesn’t come for free…). I do know that this post still doesn’t answer why the pitchbend becomes insensitive in first place and that it doesn’t offer a real “DIY” solution… 
Feel free to ask any questions!
Cheers.
):