OK, guys, my cruise control worked, then started to not work every now and then, and now it works only once every two months.

Any ideas?
Thanks!

 

Just a huge guess, but it sounds like the dump valve not closing.
There is a vacuum valve usually controlled by the brake pedal. This
valve is shut when the brake pedal is not being used, when you
put on the brakes the pedal goes down and the dump valve is linked to it, at this point the valve is opened and lets off vacuum
and the cruise stops working untill you reset. Different make vehicles will have about the same set up but may control the valve
in different ways, just have to look and see.