Hank,
They can be very tight at times.
Application of a penetrating solvent like Kroil, and then spot chilling of the extension can be helpfull.
There is a product on the market for janitors called "Gum solv" that is essentially nothing more than CO2 , used for removing gum (Freeze, clobber with hammer and vaccum)in a shag carpet.
The stuff works great for spot freezing.
Another product that works well is Radio shack "Dust remover spray" that is used on computer Key boards and the like.
Turn the can upside down so the liquid content comes out, and apply directly to the area behind the reciever.
INSTANT frozen!!!!
Combined with Kroil that has been allowed to soak into the threads for 30 min, I have yet to have one fight so as that I have given up.
Best of luck!
S-28