as I always wondered about this info, I went to Walter some weeks ago to ask him, what he does when traveller leave their bikes there. Answer: Nothing!
The custom problems, which you will have parking your bike longer than 6 month are your problem.
I have seen some Argentinians with a camper having problems because of being three days over time! I think they paid a bit to the customs, but that might not always work.
In addition you are not always automatically getting 6 month - ask for it. And even then, they like to reduce to the end of a month, so that you have 5 month and some days.
Saludos de La Paz