Don't forget that you may be able to clean out the solenoid before you need to change the coils. The door lock solenoids are not polarized, but work in a push-pull manner depending on the polarity of the applied voltage. After all of this time (8-10) years for some of you there could be an accumulation of rust, scale, mud, e.t.c in the solenoid plungers (coil); which will eventually bind on the plunger stopping operation.
I have a 11 year old unit that I recently performed maintenance on all my Lock Motors (solenoids) However by getting access to them I was able to spray Electrical Contact Cleaner onto the plungers which restored them completely. In some cases this did not require removal or replacement of the Lock Motors. Perhaps you can try this before a replacement is required. Caveat: one clean do not spray "3-In-One",Carburetor Cleaner, e.t.c. oil into a solenoid under any condition.
