Hi guys, i have a couple of questions about my 1991 nissan nx 1600 that i hope i can get some answers to. Problem #1 , mY engine bucks at certain speeds, like ranges 38-41 , 68-71 mph etc. The car is well maintained and tune up is up to date. i have owned it for over 4 years with this problem. it hasnt gotten worse but only just alittle better. Problem#2 ,there is also some oil a the bottom of my distributor where it bolts to the engine. Might that be causing it? I have replaced the distributor a couple of years back with a used unit and the problem is still there. Problem#3, my #1 spark plug has some oil on it. Is it a hard job to replace the front valve cover gasket and seals? and is that what they refer to as the head gasket? the car burns very little oil and has no leaks. i have lost alittle coolant from the reservoir from time to time but oil changes looks normal. The car has been extremely reliable aside from some annoying alernator replacements. I just want to tryto keep it maintained to a void any majoR problems down the road. My mileage is 162,000. Should i be concerned about my timing chain and water pump at this mileage? Thanks for any help.