The condition of the silencer in itself will not cause it to fail an MOT unless there is undue noise or there is a significant leak of gas other than from the tail pipe.
If it's corroded and peeling but is not leaking and the baffles haven't collapsed to cause a racket, then it will appear as an advisory... something like "..silencer deteriorated but not causing any leak of gas..."
I once replaced the cat' back on my old Alfa 145 with a stainless system. I decided it would be a good idea to delete the middle silencer but keep a regular silencer (all in stainless steel) at the blunt end. That was fairly loud I have to say (middle silencer actually does the main bit of noise suppression) and made me a bit self-conscious, although it never got noted at MOT time as being too loud.
Get yourself a stainless system made up, keeping any mid-section silencers your Abarth might have but use a smaller (aka "sport") rear silencer to get you just a bit more fruity. But you need to have a physical silencer for the MOT, as far as I'm aware.. it might fall foul of the new reg's about modifications that deleted (usually DPF in diesels) components otherwise.
Don't peel off any loose skin on your silencer. I think it would look more decreprit than just leaving it as it is, although trimming off any very scabby bits might be a good idea, if it prevents the MOT tester cutting his head on it.. MOT testers are moody enough already, without your car inflicting ABH on them...
And it will appear that you checked the silencer/saw it had no leaks, so he'll know you're on the maintenance... and he won't tell you it's leaking if it isn't.. since he'll know you'll know different.
Ralf S.
