Altho possible, you may not find any loose connections. The transfer switch uses springs and an electro magnet to hold the power terminals together when it is energized. On a 21 year old coach there is a good chance that the terminals have corroded or the springs/electro magnet have deteriorated to the point where the transfer switch needs to be replaced.
The transfer switch has a cover that can be removed to inspect the innards. If you DO NOT feel comfortable working around electric items, you should have an electrician check it.