HS will also sell replacement leads for you to have fitted.
Before you do that though are you sure it's definitely the lead/plugs?
One of our group asked me to look at his headset with a similar problem and a bit of metal polish on the plug did wonders for his connectivity! It only takes a small bit of grot to cause the problem.
I've also had problems with older Peltors that had a mic held on by two tiny screws. Effectively the boom terminated in a small two-pronged plug. The mic had a pair of matching holes and was held in place by two tiny screws that also made the connection. One screw done up tight prevents the mic falling off, the other being loose causes a dodgy connection. 30 seconds work with a jeweller's screwdriver to fix.
Mike