Kate.
It would be worth your while,and save you alot of grief,if you can either remove the faulty abs unit,or get somebody else to do so.Then send it off for a refurb at say BBA Remain in Rochester as they will do a full refurb on it and give it a warranty.Allyou thyen need to do is refit it and it will be sorted.
IMHO I think that would be a safer option and alot quicker.It should cost sub £130 and obviously a few £,s to have it removed/refited if you don,t fancy the job.I would happily pick the old unit up from you as in Caterham Tuesday evening and could drop it off at BBA Wednesday morning as I live just round the corner from them .They refurbished mine on my old 98.2.5 several years ago and I know others have used them to.
Pm if you need any help,but I did struggle removing mine so its not a job I would be looking to take on again