Start with measuring the voltages going to the displays to know if they are in spec first.

If they are outgassing, then you can move to a LED display and sell the original display as parts.

Agreed ..check voltages....... More specifically...I would check the 39k ohm resistors on the power supply as they are known weak spots in these and system 11 games. If they are out of spec .....replace with a 1 or 2 watt flame proof version and I will bet the displays will work just fine

Yes, they can be repaired.
Read the DMD repair section on this site:
http://techniek.flipperwinkel.nl/desega/index3.htm

...But then scroll down to the "Alpha-Numeric Display Problems" Section as your DE Simpsons uses a 2-line Alpha-Numeric display.

Replace the two resistors they mention as I have had two displays I have repaired that looked like an outgassed display (garbage,blurry,etc.) but the two resistore fixed them up nice and clean.

yup thats the first thing I asked him to check after voltages. They are undersized and need to be 1 or 2 watt 39kohm.

It wouldn't hurt

yes. They are undersized for the job they need to do and are VERY tired and old.. Put flame proof 1 or 2 watt versions in. And then retry the display. Sometimes it just helps, even though they 'meter' fine

hmmm thats a tough one. Tricky to do... You can carefully bend the metal so it rests against the glass again and solder it up...OR use conductive paste epoxy to cold weld them back in place.
But it is a tough thing to fix. Sometimes you can grind/chip a little of the glass away and solder a jumper there. You can also use standard metal tie wire to extend the legs to give you more to play with.
I have had the best luck with a minor bend and solder and worst case also using jumper wire.

if the voltage readings are good and strong. then yes it is outgassed and no good anymore. Pick up an Xpin LED display and do not look back. Looks better than factory

Good Job. you will not regret it. Brett at Xpin is a great guy and stands behind his products. Once you see how good it looks you will want them for every game.