theres 2 seals on the 16v dizzy, you got the nice easy big green un round the outside which is piece o wee to change, then you got the one inside the dizzy which involves strippin the whole thing down, which is a right pain in the arse. Oil leak on its own prob wont casue the problem, unless the inside of the dizzy is completly sopping with oil! Mine leaked pretty badly but it never caused these symptoms.
pop off the cap and give it a damn good clean, check the rotor arm and cap[ contacts for carbon build up, give em a bit of a clean up if its bad with some sandpaper.