Workhorse chassis has a known intermittent problem with the Switch units in the steering column. Do some back search of old posts and you will find some mention of it. I had a 06 W22 which would sometimes not turn on the flashers and sometimes stop having a right blinker. Do some basic troubleshooting and pay close attention to the Multi-switch in the steering column. It does a lot of work in a small area and is subject to constant movement and use. Just a thought.
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26795818/gotomsg/26796929.cfm#26796929