The increased time between re-boots is likely because the device is trying to "reconstruct" region 41 with basic information however logically if there was previously bad data in region 41 which was causing the bootloop it would now be frozen on the logo screen. That's because it's had cure fw written to region 14 previously so clearing potentially poisoned data from 41 should allow 14 do its job. Therefore something else other than 41 is causing the bootloop and that's now narrowed down to one of these possible problems:

(a) A corrupt essential file in the file system (i.e. those files normally seen in Mass Storage Mode). That could even be a general data corruption as sometimes happens where 'nonsense' folder/file names appear in flash drives... but more likely caused by a single individual bad file such as, for example, a map IMG file, a poi GPI file, or a voice VPM file, etc. Unfortunately, that's by far the least possibility because the cure fw in region 14 should have prevented any attempt to load such files at all.

(b) A hardware fault such as a partially failed flash chip .... which is definitely not fixable by any software means.

(c) A foreign bootloader is present in region 5 which now cannot be overwritten from region 12 apparently because many flash attempts have been made by you using the correct ramloader (the so-called boot.bin). You'll recall that the ramloader is written to the virtual region 12 and it then writes to the physical region 5 (but that's done on the next successful complete boot cycle). So even though we're able to run commands from SD using boot.bin as an RGN the incapable bootloader is still in region 5. Region 5 is protected from direct flashing in every Garmin device i've tried (i.e., writing 5.bin via SD command "xrgn,5,1:/5.bin" will fail).

In the slight hope that it might be (a), if you want to examine the file system you can dump it using "copydir,0:/,1:/BackUp/" command and then try writing back completely empty folders corresponding to those in the dump, i.e. .System, Garmin, etc, etc., to overwrite all the existing folders ("copydir,1:/.System/,0:/.System/" and "copydir,1:/Garmin/,0:/Garmin/" etc.). Or if you can see any obvious corruption in a particular file from the dump it can be selectively deleted using del command, e.g. "del,0:/.System/gupdate.gcd" to remove a bad GCD file.

Personally, i'm now much less hopeful than optimistic that the device is saveable, but good luck.