Re: clutch starts to engage while lever is fully pulled in after a long ride?
If you've followed the clutch adjustment procedures correctly then you might be right about the cable slipping/stretching.
If you have a hobby shop near you you can find a good replacement for the cable stop. Ask for a 1/16" wheel collar. They are used on model airplanes on the axles to hold the landing gear wheels on. They typically have Allen head cap screws in place of the slotted screw that comes in the kit.
Here's a suggestion: With a new or replacment clutch cable, leave the clutch lever in the locked (clutch disengaged) position when the bike is parked and not being ridden. This will hasten the cable stretch process so you won't have to do it as often. All cables will stretch a little. The force needed to actuate (disengage) the clutch is more than standard bicycle brake cables normally see. They will stretch a little and it doesn't take much to adversely effect clutch operation.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"