Top spray arm kept falling off

We noticed after only a year that the top spray arm would keep falling off during a cleaning cycle. We'd find it in the top rack of the dishwasher. When we needed to have the motor replaced after only 14 months, the repairman told us this arm falling off is a big problem. He repaired it the best way he could. Recently when it came off there was no way to fix it ourselves and we had to order another part. It's very easy to install as it just screws on the way a hose screws on to a spigot.