1997 Ford Taurus Bad EVAP valve already replaced

Hi, thanks for a really great website.

I had a computer diagnosis of a "bad evap valve" from a mechanic I trust 3 months ago after the check engine light had been on. The valve was checked, found defective and replaced.

The check engine light stayed off for a good 500 miles, but then came back on again. The mechanic I had originally taken the car to is far away and difficult, though possible, to get to, so I took it locally. I got the same computer diagnosis, sadly, of a bad evap valve.

I didn't have the repair done yet and called the original mechanic who said they would look at it again without charge.

Taking the car to the original mechanic though requires 2 days off work, one to drop the car off and one to pick it up, so I'm still thinking.

I've owned this used car for about 5 years with very few problems, and none major.

I did have a diagnostic done a couple years ago by a mechanic I trust less that he said showed a bad 02 sensor in front, so I replaced only the 2 upstream sensors. That code doesn't show anymore but I wonder if that could still relate to the current code and I should replace the downstream 02 sensors as well (I know I should replace all 4 at once but it was too pricey)

I haven't ever had a tuneup on the car though I was told several years ago the spark plugs were fine and should last to 100,000. However, reading the tips and forums here, it sounds like a tuneup is a good idea. Could that actually be the root of the problem?

Or something else could cause the bad evap valve code?

Edit: Just looked up the code from the recent repair and it is as follows. I don't have the code from the original repair and I see there are a number of codes regarding evap valve, so maybe this one is different?

P0443 Evaporative Emission Control System Purge Control Valve Circuit Malfunction

A brief 2nd question, my turn signal indicators will flash unevenly, sometimes very quickly at first (double speed) for a few seconds, and then at normal speed. Any thoughts on that? I did have a new a battery and remanufactured alternator installed prior to experiencing this problem. Also a new serpentine belt.

I'm no mechanic so I'm looking for the best way to get the evap code issue fixed permanently.

1) Just replace it again locally and hope for the best?

2) Take it back to the difficult to get to place and have them look at it again?

3) Thoughts about what else could cause the code?