Fit for purpose is a bit of a joke. Fit for a sunny Sunday on the Solent maybe but rarely on a long distance cruiser. I think you'd be hard put to get anywhere with a claim, there's too many variables.
Warranty claims, on the other hand, should (should) be easier to deal with. I have a theory that most suppliers reckon long distance cruisers will just give up, because it becomes too expensive, time consuming and difficult to pursue a warranty claim long distance. That said, if there is no possible get out (for the manufacturer) then I think the warranty would be honoured. The problems come when the manufacturer can claim the organisation that fitted the equipment fitted it incorrectly.
Incidentally, there is a web site called 'F P's are cr*p' (full makers name). Trust me, you're not alone with your problems.