Hydraulic brake bleed fail - try again or replace?
I'm only going to answer an aspect of your question; you can apply it to your brake how you wish.
Firstly, Certain Tekro models are fiddly to bleed but also feel like they need bleeding if the pads are worn down, so if you haven't put new pads in, I suggest you do that first.
When something like this comes into a commercial workshop and this amount of time has effectively been wasted, there's a strong argument for replacing the brake, giving better value for the customer and putting the mechanic's time back into another job that pays the bills.
When you are in another scenario where conservation of materials is important and you are time rich, you can play with bleeding this as long as you like, though you may already have learned all you need to know.
Meanwhile, SRAM Level, Shimano's entry-level hydro brakes and even new Tektro brakes are easy to set up, easier to bleed and don't cost very much, especially when compared to a workshop hourly rate.