What game? Is it an entire column, or just a few dots out of the column?

Have you tried reseating the ribbon cable on the DMD board?

That's the first thing I would do.

If it's the last row of the display, it could be a broken pin. Earlier DMDs have pins like old tube displays - newer ones use ribbon cables. The pins sometimes break where they enter the glass. But, that would only be the case with an entire row, not a partial row.

Perhaps you could have the seller do a display test, and verify whether it's the entire row, or a partial row.

The display test also checks the display RAM at the end of the test.

Display RAM and a socket are $5, if you have the tools/experience to change it.
Broken display pin sometimes is fixable, sometimes isn't. Depends at how patient you are and how good you are at it. I've had poor luck with that myself, but know many collectors who had just fine luck doing it.

Sometimes you can get lucky and just re-flow the solder at that pin controlling the row.

Hit and miss like John said.

It is outgassing.

If an entire row or column is out then the it is a broken pin and can be fixed.

This is a partially lit row and is a classic sign of outgassing. New display from pinball life should run you less then 150 if you get the machine.

There is a chance you can try it in another game and it may look fine. It all depends on the condition of the hv section. Some are stronger then others which may supply enough voltage to light the dim areas, but I would not count on it.

Very likely to be connectors. To me if the display were outgassing the other dots wouldn't be so fresh and bright.

If it is the entire last row look to see if the dmd uses ribbons or pin style for the connection.

If it is pin style it is probably broken off at the glass. Go to nappa (autozone and oreilly dont carry it). Ask for a defroster repair kit. Make sure it has the conductive paint inside it. Sand the display where the broken pin is. Just a light scraping to expose the pin in the glass. Put the paint on. Make sure it is only touching that pin as if you join pins you will get lines going on when they shouldn't.

Press the other end of the pin against the paint. I recommend testing it in a game first to makes ure it has a good connection. If so superglue it in place.

If it is ribbon you can use paper to press the ribbon against the contact. There is also a conductive tape that 3m makes. I have never used it, but Borygard told me about it at the ohio show.

It has no bearing. I have had several that the displays look perfect, but on certain screens a few dots won't light or flicker. The rest of the display looks brand new. Right now my nascar does it, but unless you really pay attention or know what screens exhibit it you would never know.