If the segments are OK (numbers all readable) but just getting dim on one side, then I am 100% sure this is JUST a bulb concern. The display is backlit LCD, it uses 3 bulbs, left, right and center, so the dim side just needs the bulb. I recommend doing all 3 at once.
PS: There are 3 clear bulbs and 3 red ones for when the display shows a red warning message, just do the 3 clear ones, the red ones are seldom used and don't think I've ever replaced a single one. Clear ones are for the normal amber color.
Gilly

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