Replacement Coupler

If your coupler gets sand in it, clean it out by alternating between spraying water into it and connecting/disconnecting it from the stud.  This will help get the dirt out.  Once it is working smoothely, blow compressed air into it to dry it out.  Do not lube it with oily lubes as they collect more dirt.  You can use a drying graphite lube spray.  If this doesn't work you can buy this replacement coupler.