Your gearbox might have bad or the wrong oil, changing your gearbox oil (80w90) will fix this. Also look for any metal in the old oil as this is signs of a worn our grearbox.
Or
It could be your clutch isent allways disengaging, does the pedal feel or release point change?
And with the leaking timing cover if it isent leaking on your belts or having to top up the oil every week, thats fine. If it's leaking from the same spot there has to be an imperfection on the cover or housing. If you cant find it or fix it, try a decent liquid gasket.