@ilmai I think I found a really good solution :
2 recorders recording CUE, 2 chained patterns.
Edit : 1 pattern suffice, limited to 32 steps per loop (scale 1/2 possible to double time).
Works flawlessly! 
Pattern 1 :
Track 1 plays Recording 1
Track 1 CUE send
Recorder 2 records CUE
Pattern 2 :
Track 1 plays Recording 2 (soundlock)
Recorder 1 records CUE
Agree with @sezare56 I do this all the time with my loopers. I use the cue out to my guitar pedals and then record the mangled loop. Now the only thing you have to figure out though is what your inputs are “listening” too in your loopers. If you send something to the cue and have it come back thru the wrong input you’ll just get feedback.
You can also get some interesting results using delay. With cue in studio mode, set up a thru machine recording from cue, with a delay with DIR set to 0 (with no feedback, to begin with at least) and use the cue level for that track as your feedback control. You can send other tracks to the loop with their cue levels, use other thru machines listening to cue as parallel effects in the feedback loop, and for series effects in the feedback loop you could use a neighbor machine AFTER the track with the delay, and use the cue level of the neighbor track as your feedback, so any effects on the neighbor track are inserted into your feedback loop.
You could also have multiple thru tracks set up as loooping delays with different delay times this way, although you’d be somewhat limited by having to share cue as your feedback path (panning could help here).
Way less flexible than flex machines in terms of recording and overdubbing possibilities but it introduces all sorts of other possibilities (and you could also try combining it with the thru machine techniques). I haven’t really done much with it yet myself but enough to see plenty of potential.
I think I remember checking that repeated resampling slowly destroys the sound even with the fx taken out. Probably not an issue in this use case but just wanted to mention it.
Yeah like I mentioned above, even with “None” selected for both FX slots, the resampled sound slowly gets louder until it starts clipping and gets destroyed. This happens far quicker if Filter is selected, even if wide open.
I don’t think @JSZ meant misaligned gain staging destroying the sound. Even if the gain staging is perfect it’s the fact that with each round you run through A/D + D/A conversion which will destroy the sound in the long run.
I cannot see it would go thru the codec if your overdubbing - you would assume this would all be kept in the digital realm… only if you went out thru outputs and back into the inputs would this occur.
the only thing i can think that the adc part could ‘mess’ up, is that each time you record you are taking in more noise from the analog realm… perhaps that can build up.
but, this should be a ‘perfect’ process, but its alway possible that same part of the algo is not lossless - though if no fx, and time-stretching is off - Im a bit surprised.
Wasn’t it the case that insert effects (especially filter and lofi) - even at neutral settings degrade the audio over time and send fx (delay, reverb…) don’t.
Of course, you are right here. When just internally overdubbing this will not happen. My looping setups almost always involve some external analog gear as send effects, but of course that’s just me and my setups.
With FX set to None?
Wrong settings then.
With my method it gets very slowly lower.
I’m making a test, with 16/128 VOL increase with an lfo.
Since 10mn, the sound didn’t change noticeably : I’m checking it with the same sample out of phase.
Good call, I’m fairly sure I had time stretching still enabled even though it was at a neutral setting. There are quite a few details to take into account to make this work!
So @ilmai you’re not interested in a working solution? 
Work with 1 pattern, 32 step loop, which can be doubled with scale 1/2.
I didn’t quite get what the benefit of this was compared to just using a single record buffer?
@ilmai That way you’re totally free to mangle the loop!
With 1 recorder, the playback is stopped if you pitch up, reverse or timestrech it.
With 2 recorders, once recorded by recorder 1, you can mangle recording 1, reverse, pitch, anything, while recording it by the recorder 2. Then the recording 2 is played, and can be mangled freely while recording it by the recorder 1.
Etc.
Recorder 2 records buffer 1
Recorder 1 records buffer 2
I just recorded a 1 bar loop with a sine with a recorder recording CUE continously during 20 mn, recording being sent to CUE. It gets progressively noisy with artifacts, but I think it’s still usable. 600 passes!
Of course it’s better with less passes!
Would love to hear these artifacts - easy for you to record?
Slow roasted audio 
See also (related): https://www.youtube.com/watch?v=cVy9ABT5-iY
Artifacts on the sine are not really interesting.
I heard it was possible to record with the OT…
Exemple of Destructive loop. beware, it goes crazy. 
haha, I think you got a high score in galaga at about 1:50
huge smile on my face - long live the OT
Nice.
And again I am reminded of my early realisation with octatrack.
It really does not matter at all what the source material is. You can literally transform any source, into anything you can imagine with OT.
Yes! I was playing the recording with the chromatic mode, but I forgot to press Function to avoid to retrigger the recording. So it stopped to record. Had to play like crazy to feed the loop again. 