Sure that is not the grain of the wood ?

Your options are live with it, pull and have it restored, or look for another and sell this one when you bet a better one.

It doesn't look bad, and I may be wrong, but a regular clearing of this PF might eliminate the issue without extensive work.

Agreed. Planking you can't do a thing for. All you can do is try try to stabilize it or pull the playfield out for a full restore.

Keep the game somewhere with controlled humidity and temp.

I also believe that keeping the playfield protected by a good application of quality wax will help stabilize.

I can't answer that from experience, but my guess is that a clear would just "seal in" what's there, and not hide it.
You need a restoration fellow to actually sand down and rebuild the artwork. But again, that's just my guess. Not my area of expertise.

For small lines, yes is my understanding. I don't think in a stable controlled room temperature it would get any worse. Maybe one of the restorers here will chime in.

First question is if it has gotten down into the paint. Put some Naptha on it and see if everything looks good or it still looks like crap.

Yes.

I'd use a magic eraser and some Rubbing alchool 92+ and give it a good scrubbing (be careful you don't want to take the paint off but try and get in the tiny cracks. Since the area seems fairly even for colors (blues and blacks) I would paint over the affected areas. And then since you would have all the playfield off, I'd get it clear coated.

well if you want to even the swell you will have to sand the paint down and put bondo in the places that create creavices.

I ask this as a newb, but is it normal to see the grain of the wood in playfields, especially on lighter colored paints? I noticed what looked to be the grain on an Elvira and The Party Monsters I was looking at, mostly on the skulls in the outlane. I'm hoping it's not planking.