I will check when I get home. You modified the mtd6 file for me about a month ago.I'd say it's worth trying.
Admittedly the sample size of original 5.2.8 firmware is small (3)so far - but the analysis was based on looking in the firmware at why such devices can resist being updated.
This was the 'enhanced mtd hack' where the 0xFF98 devType is corrected, and the checksum is updated?