I can confirm that the method linked below for the Sony RDR-GXD360 worked on mine. In that I can now play region 1 and 2. Haven't tested for other regions because I don't believe I have any other disc types. I am pretty sure it is region free though from reading the threads here.
Sony RDR - HX510 Region Free Hack
As said somewhere else the REMOTE.TXT file mustn't contain spaces in the numbers, no word wrapping and there should be a carrage return ie [enter] after the last line (line 5) in the file. I have uploaded the file that worked for me.
I'd also like to point out that it was after step 9 that I got the "TIMER OK" message.
Hope this helps anyone interested.
Thanks goes to the useful people here.
@ Admin, Mods- I thought I saw a library type thread somewhere listing all the different models region decoding was available for. For some reason I can't find that now, so please update/move/edit this post as you see fit.
Thanks again.