1994 Corolla does not accelerate

I have 142000 Miles on the clutch, because I dont remember changing the clutch. Is changing the clutch fairly expensive? Would it imply removing the transmission and changing the clutch plate? Is changing the clutch fairly common on Manual transmission and what are the steps one can take to avoid it.

I changed the air filter and the problem did not go away. I have not changed the fuel filter ever. Could it be the air sensor or fuel filter. I checked the distributor cap and one of the spark plugs connectors had some kind of oil/gas where it connected to the distributor cap. There is definitely oil leaking from this connector because there seems to be lot of oil on parts below distributor cap. I was wondering if the leak is repaired why would I still need to replace the clutch. Wouldn't the oil burn away by friction? I was checking on the internet and some one mentioned that changing the clutch could cost $800+ which is a lot of money. So is it worth spending money on changing the fuel filter ($100) to see if it fixes the problem or based on the symptom do we know for sure it is not the fuel filter? Please Help.