A 'rebuild' as distinct from 'mending' should give you an as new fully tested unit. Your Insurance company should give you legal costs cover and be able to appoint a solicitor to advise you. I've noticed that when the first sturn letter goes in, things spring into life. The enginneers liability insurance will cover them (if they have this - and they should as a business) so in reality they will loose little.............. but a little face maybe.
Wish you well with this.