I am fortunate that I have not had those particular problems, but I bought the 156 Sillyspeed with the ABS warning light on. Not having the equipment or inclination to sort it myself I took her to a local Alfa specialist (Alfarama) in Stanmore, and said "check the fuse first". (BTW dont drive fast with the ABS light on 'cos it will swap ends under heavy braking if you are not ready for it!)
Well it was the fuse and the man put it all right and told me "Your battery is not the cars original (which I knew) and is not man enough for the job. That can cause all sorts of problems with the computers and sensors", so on my approval he fitted a new, correct, Bosch GEL battery for about £75. MUST have known what he was talking about, huh?
Oh, and further, in fifteen years of working at Alfa, BMW, Vauxhall and Honda dealerships, various Alfa specialists and race prep places and also doing family & friends cars I have NEVER come accross an ECU that actually needed replacing. I have seen them replaced but it never cured the problem. Loose earths are always worth looking for however!
Paulus