Nissan Repair: 2000 Altima - rough idle, spark plug wires, valve cover gasket

Question
Just got back from a service station.  Went in thinking I needed a tune-up (90k miles) because my car idled roughly in gear and neutral but was fine when in motion.  I suggested the tune-up.  The mechanic performed a minor tune-up (changed the 4 spark plugs....I could have done that) and then told me that my number 4 cylinder was weak at idle and that my problem would persist unless he performed other diagnostic checks that would cost $100 to start.  He thinks it could be a fuel injector but was saying other things and $$$$ signs were flashing in front of me.  Seems Nissan built the engine in such a way that a whole lot of parts need to be removed to diagnose this problem.  He also said that there is a bit of oil that gets into the spark plug shafts (#1 and #2) via the manifold gasket or from the shaft itself.  He showed me the oil that accumulates at the tip of the spark plug wires.  The SES light was on for a while and do you believe it....it went off an hour BEFORE I brought the car in!!  The light is no longer on at the moment.  I put some injector cleaner with a full tank this morning.  In years 1 and 2, I used to use the highest octane....but with the raising cost of gas, I have been using regular gas the past 3 years or so.  I do regret not putting premium this morning with the cleaner though.  Otherwise, the car runs fine.....except for those nagging Year 5 problems (headlight, battery, tail light, interior light, window switch, interior trunk light, etc. etc.).

Can you please help me.  I would like to do some of these repairs myself if I don't need any special equipment.  I used to make minor repairs to my older cars but haven't touched these new ones anymore.

Answer
Gerry,

Oil on the spark plug boots is the valve cover gasket starting to leak.  If it is only a seep it can be left for a time.  If you like you could change the gasket.  The injector on that cylinder can be replaced.  I like to get to the bottom of a problem and if that cylinder is weak due to fuel starvation then I would replace the injector and you could do that too.  It is not difficult.  just buy an injector and a set of o-rings and only replace the one that is derfective.  I like premium but it does not help with defective injectors and it only helps to keep clean injectors clean.  So, if an injector goes out and it is not plugged then just replace it.