Nissan Repair: A Few Engine Questions, nissan altima, photo sensor

Question
I have a 1993 Nissan Altima, manual with 224K miles which I've owned since 44k miles and plan to keep for as long as possible since it runs great.  I have a few problems I would like to identify and resolve.  First, my check engine light comes on and stays on for a little while and then goes off by the time I want to have someone check it out.  However I managed to get it to the dealer and they said that EGR had 3 errors or somehting like that.  Also I sometimes notice a natural gas smell in the car.  What do I need to do to fix the EGR and could this ocassional natural gas smell be attributed to the EGR?  Could it be the manifold exhaust leaking and how can I tell?  Second, I noticed that my car was stuttering when I was driving almost like the gears were not catching when I gave the car gas.  Shortly after the car would not start and was diagnosed a bad distributor because oil had gotten into it blocking the photo sensor.  Just had it replace 2 days ago along with having the timing resynced.  My question is does just a new distributor keep the oil in the engine from getting to the photo sensor in the distributor?  Is it becasue of the seal on the distributor?  Third, I noticed that my car when idling has a slight squeek/chirp like something is loose.  My neighbor who is a mechanic said since the car has 224K on it that the timing chain is stretched causing the noise which he said is not anything to worry about and that when he replaces my front cover by the timing chain he will replace it along since he will have the engine apart.  Can you think of anything else it could be and what else should be replaced when changing the front cover given the mileage?  Could it be related to worn motor mounts?

Answer
The EGR could cause the idle problem and the stuttering.  The distributor is a common thing on these cars and the distributor does keep the oil from getting up in the distributor by use of the seal.  Replacement of the distributor requires the car to be retimed.  Te squeek noise could be caused by the air box rubbing at the strut tower.  This is common and can be checked by having someone start the car and put it in drive and then put your hand on the filter box.  If the noise goes away you have found the problem.  I have seen several like this.  Changing the chain at this time would be within reason and besides the cover you replace the tensioner if it is worn and the front seal in the cover.  But, that will be new with the cover so you should have it all.