I would take a completely different approach to sort out the issues of:-
1. A hire bike that you don't own
2. A 2012 model
For 1, does the hire company in Spain hold a deposit? In any case, depending on the small print of your contract with them, I would be placing the responsibility on them to sort out your bike - break down cover basically.
For 2, BMW have a comprehensive 2 year warranty on all of their bikes; the problem in this case is that you don't own the bike - nevertheless, get the BMW authorised dealership staff to take responsibility for the warranty issue, in conjunction with the actual owner.
"Threaten" to bring a lot of poor publicity down on the heads of both of them. After all, you are on vacation, and between them those two are responsible (subject to your actual hire contract).
Hope this is at least food for thought!
ps At the very worst, the break down cover of the hire company collects the bike on trailer and returns it to Spain while you finish your vacation with a hire car - lots of UK based break down cover provides this level of service.
__________________
Dave
|