Hi All...
Devils Advocate time!...
Any car hire company offering insurance cover for gearbox clutch damage due to misuse is simply putting the frighteners on clients.
Seriously... when did your own car suffer a clutch or gearbox failure due to misuse? A clutch should last at least 80,000 miles.
Car hire companies generally trade in their cars at 12,000 miles or 20,0000 Kms. Most hire cars will reach this figure within 6 months of rental use and the original warranty with the vehicle ensures that they will be sold on before the warranty expires. For a while I worked for Hertz in the UK and cars were replaced between 8000 and 10000 miles.
Speaking as one who regularly commuted 150 miles a day six days a week for fifteen years, I can truthfully say that in all that time, plus routine domestic and social travel, I got through three cars, with 250,000 miles on the first, 90,000on the second and 145,000 on the third. Thats the equivalent of travelling to the moon and back... I replaced the clutch on the first and last cars (from choice not necessity) at 125,000 miles. Never once did I have to replace a gearbox.
The car hire companies mentioned in this thread have latched on in a big way to the same sales techniques used by the low cost airlines. They will try to screw you into making additional payments for anything they can dream up.
Dont let them frighten you...They would have a hard time proving negligence...Tell'em to stuff it, along with their Underside damage insurance, although If you find that windscreen replacement is rolled into the same additional policy then the choice is yours as to whether you take on the policy.
To the best of my knowledge the Spanish road authorities dont use the loose chippings so beloved of their British cheapskate counterparts, so the chances of losing a windscreen this way are somewhat lower than in the UK.
Just treat continental sleeping policemen (Paso Elevados) with respect...