It's possible that carefully removing and putting back the display could improve things. Best to remove the batteries before doing it.
The readout on mine was not very clear. I removed the top of the finder and could see the long rectangular mirror was dirty. I cleaned all the mirrors and glass surfaces. The display looked great after that. It seems like the problem is intermittent, so probably this will not help, but I did find that my exact eye position made a difference before I cleaned it.If its still not bright enough just get another finder.