How many miles you got on it?
Like ty8ight says, if it's not the cable, you are are due a new clutch. Bad oil will do it, but changing the oil and hoping it'll recover is really only a trick for when you're up the desert, you'll need to take something like half the life off a contaminated clutch before it'll be 99% right, which might get you to civilisation, but is false economy if you are already there. If you are above 50,000 miles and the plates come out looking thin it's just wear. If they come out looking glassy or burnt but with lots of wear left you need to change the brand of oil and have a good look at the springs, centre, actuator mechanism and so on.
Could be worse, I've got to take a sidecar off to get at mine