lol it wont do mate i had exactly the same if you have a search through my threads i'v posted i had exactly the same it wasn't uniform i didn't think it was the clutch at first but fitted one just to rule it out and it cured the problem straight off, the clutch wasn't even to the rivits neither and also it never slipped i just used to get a problem selecting gears every now and again like said it'd mainly get stuck in 4th for me but when it got really bad it started to do it in most gears, i was told the selector and that but if it'll still select gears once engine is off then the linkage should be fine.

try the gearbox oil first as it's the easiest and cheapest but then i'd be looking at your clutch, when was it last changed and how many miles has it got?