I have a 2007 GSA (non servo) and the Brake Failure Light started coming on recently albeit intermittently. After much internet search and looking here on the forum I contacted
https://www.motoscot.co.uk/ who are based just outside Luton in Bedfordshire. (I know its a way from you in Portsmouth but possibly worth a call) They were confident of being able to repair the unit and I took my bike over this morning and after a friendly welcome and a mug of coffee surgery began and within minutes all the plastic and fuel tank had been carefully removed and the ABS unit extracted for closer inspection.
Anyway it transpires that one previous owner had already had an attempt at fixing this fairly common problem but whatever they had done clearly hadn't worked properly but despite this the guys remained optimistic and put their wealth of experience and knowledge to work.
Within a few hours the unit was being put back together and transplanted into the bike once more. After testing all systems were working as they should and at a fraction of a new ABS unit which I understand is about £1500-1800. Ouch!
Very happy and will certainly be using
MOTOSCOT in the future and without hesitation wholly recommend them you.