I think it's worth a try. I got "lucky" when I sarned the solicitors who did the repo and the re selling of my home. The first reply was standard third party stuff.can't disclose. But I wrote back and said I would make a complaint to the IC if they did not respond in accordance with the data protection act. This prompted them to send me every single viewing sheet they had from the estate agents they used and this information demonstrated that my lender was not truthful re the interest in my home. The lender had said the market was sluggish and that there was only 3 viewings. The information sent from my soliciter showed that there was TEN viewings and even gave names and contact numbers. In addition to this their information showed that there had been two offers on the property instead of the one the lender said there was.(posted 7610 days ago)This might not seem very important but for me it demonstrated that the lender was not accurate and truthful with the information they provided...and at the end of the day if you can discredit these people in any way it might prove useful should you get to court.
You make your own choices but I would advise you to SARN everyone named/involved in your case.
You have nothing to lose and hopefully something to gain.
I would add that I did send my SARN's by recorded delivery but I did not send the £10 unless they asked for it. So the initial process need not be expensive!
Good luck!