Need Advice

I have a 96 Neon with 140,000 miles on it.In the past year, the service engine light has been on and off - (on for a few weeks, off for a week or two, and back on again).The code says "cylinder one misfiring - lean fuel/air mix." There are some hesitation here and there when stepping on the gas.I have tried putting in new plugs/wires, changing the fuel filter periodically,and having the fuel injectors cleaned.(Did improve for a few months after the injectors and the rail had been cleaned).Noticed the best thing is to put in a bottle of fuel injector cleaner from time to time -lately I have had to put the cleaner in every week. In the last month or so, idle is bad in the morning. The engine stalls easily when I let go of the gas peddle. But idle would improve and be back to normal after the car has been driven for a while.Sometimes, idle sounds weak till I put in some fuel injector cleaner. One mechanic found oil in cylinder one and claimed that oil leak in the engine was the main probelm. He said it wasn't just the gasket, and he would have to open up the engine block to seal off the leak if he could. I suspect the problem is more to do with fuel delivery. Is this mechanic right or should I go somehwere else for a more thorough engine diagnostic? The body looks like 4/5 years old - trying to hold on to it as long as I could.