OK, Here is a small time DIY, or more just an explanation what can happen after 10 years so you can know what to do about it when it happens.
Here are my old parts, two cables - part #7 and #8, locks - part #15, are upside down (pic is missing a cable going to the inside of the car, called Engine Cable Mechanism, part #6, other two cables are called 'bowden cables').
http://www.realoem.com/bmw/showparts.do?model=AM53&mospid=47723&btnr=41_1099&hg=41&fg=35&hl=1
Zoom on the passenger lock, as you can see - pretty ugly, especially where the cable hooks into the lock - the corrosion has bonded the two things so I couldn't even remove the cable from the lock for cleaning, hence I decided to get a new lock (also for another reason, next pic...)
Zoom on the "main" driver side lock. This one serves a dual purpose. It releases the driver's side of the hood as well as pulls on the Center Bowden Cable (part #8) in order to release the passenger side of the hood.
As you can see, what happened in my case that almost screwed me up huge time, because of extra work that this lock has to perform and due to age, the main plastic hook (each lock has two) broke off - severing the main connection of the linkeage with the locks. The cable has this cylindrical connection that catches into the plastic hook. That's why my pulling with inhumane force from inside of the car resulted only in doing permanent damage to the interior cable (#6), which was fine to begin with, as no corrosion gets to it. There was no way this pulling could do anything, as there was no connection. So extra damage, worth $50 CAD. That's also the reason I bought a new passenger lock - to make sure the plastic hook was brand new, as its failure (breaking) would only allow me to open the driver's lock.
Here is my temporary solution that I came up with once I finally opened the hood and removed the locks to see what had happened. I used a strong wire to connect to the main driver's lock so I could close the hood and get to work for the next couple of days. This allowed me to shut the hood and be able to pull on the wire - which was sticking out right in front of the driver's headlamp - in order to release both locks if needed. This worked pretty well, I was able to open and close the hood several times before the stealer could get all my parts in. All in all, 'only' $200....
Now, don't ask me how to open the hood when that happens. The only hint I will give you, you can rather easily open the passenger's lock through the grille bars. You need long thin pair of pliers and a long screwdriver. You catch the wire through the grille and use the screwdriver to push them (holding the release cable right by the lock) towards the centre of the car along the cable. This will easily release that lock. How to unlock the driver's side??? Beats me... I think I must have said enough prayers... There is really almost no way you can do that from the outside. I was is such despair that I started pulling aggressively on the passenger side of the hood.. I thought I might break it, but I didn't care. I was hoping I would somehow force that driver's lock to let go... which it did LOL!