Don,
You have identified a very important issue, regarding this brake lines and sticking caliper pistons. I think both can contribute to the problem. However, IMHO the biggest factor is flushing and replacing the brake fluid every two or three years. Flushing the brake fluid will help get rid of particles in the brake line and in the caliper. Others that have posted in this forum have replaced their brake line. That is always a good idea, especially in older motorhomes that have not flushed their brake system regularly.