RN10211D flashing power light

Gazmeans wrote:

subsequently the power light now repeatedly flashes twice and pauses

That is unusual, the normal LED "decoder ring" is 

LED blink behavior for 2 disk systems is three quick blinks of all disk LEDs and the backup LED, followed by an 1s delay, followed by a number of slow blinks. 

The number of slow blinks will be the error code. Current error codes: 
   1 - Vendor mismatch 
   2 - No disks detected 
   3 - Bad contents on root partition of disks 
   4 - Flash error 
   5 - Unsupported RAID configuration

Gazmeans wrote:

On searching for a reason for this it seems it may be an issue with the SODIMM card?

No, the RAM is soldered in, so there is no such card (and no way to replace RAM).

Gazmeans wrote:

If not, can I remove the 2 disks and put them into a newer supported product?

All ReadyNAS platforms are end of life.

But you can purchase a used OS-6 ReadyNAS and migrate the disks to it.  Many 4.2.x ReadyNAS systems can be converted to OS-t, and after that is complete you can migrate to those platforms also.

You could try a risk-buy of a replacement power adapter.  No idea if that will can cause your particular symptom, but a failing adapter can certainly result in boot failures.

Gazmeans wrote:

I do very much need to salvage the data as it isn't backed up anywhere else

You can mount the data volume manually on a linux system with mdadm and btrfs installed.

You can also try RAID recovery software on a Windows PC.  Other users have successfully used ReclaiMe and UFS Explorer.  You can download ReclaiMe prior to purchase, and see if it can recover anything.

Either way, you will need a way to connect at one drive (RAID-1/XRAID) or two drives (RAID-0) to the system you are using for recovery