I see more than one potential problem here.
The most obvious one is that, whatever the alleged problem may have been “a couple of years ago”, there could well be multiple problems by this time. The Check Engine Light (CEL) will light up exactly the same whether there is one stored trouble code, or two, or three, or… Over the years, one problem could have cascaded into multiple problems. That is why it is not wise to ignore an illuminated CEL.
The other, less obvious problem is that your regular mechanic was probably not competent enough to actually know how to track down the problem indicated by the initial code that he found. So, instead of advising you to fix the problem, he told you to ignore it. This is almost surely an invalid piece of advice on his part.
All-in-all, no matter what else you do, I would suggest that you NOT return to your original mechanic.