Richard, dry metal tends to bind when put in motion so put a very thin layer of grease on the arms and you will be surprised how well it works. I do that to mine at least 4 or 5 times a year. Be sure to clean off the arms and even vaseline will do the trick. Do not leave excess on the arms, just enough to coat them. Good luck!

If you use a teflon type dry lubricant you will have a cleaner set up. You can buy a small container at bicycle shops that has a hypodermic applicator. Works well in door locks also.

Our door was doing the same thing.  I found that the door latch pin had moved in a little so the door was twisting when it closed.  I moved the pin out about 1/8 inch so the door would close more evenly and now it does not stick.  Hope this will work for you.

Tim