Another one ;o)

I have brought a second hand iPhone 3GS which is stuck in a semi-DFU loop.

I have got the device to boot with redsn0w-0.9.9b1 in tethered mode and it appears to have the firmware/baseband mentioned above

According to TU, Cydia has full blobs on file for 3.1.3, 4.0, 4.0.1, 4.0.2, 4.1 and partial for 4.2.1. [what is the difference by the way?]

I am trying to unteather the device, but nothing seems to want to work. I'm not really worried about what version I go to, so started with 4.1. Tried to restore to stock which didn't work [assume because of the BB].

Tried to restore to 4.1 created with snowbreeze which did work, but again would only booth teathered.

Normally at this point I would re-flash to a stock and start again, but because of BB 6.15, i can't.

Does anyone have any ideas?