radio display failing '98 XJ

Today for the 1st time, I noticed that the clock/radio display was going dark, periodically. Switching the power, the radio band, or
pressing the LH button to switch between the clock and radio station display did nothing to help. The radio continued playing while the lamp was out, and the lamp by the CD slot stayed lit. On a 15 minute drive, it was out for awhile and then back on a few different times. It's operating properly, now.
What should I expect? Is this a sign that that the display is about to fail, for good? Does this happen often? Is a replaceable lamp?
It is the CD/Casette/Radio unit with the 3 small graphic equalizer buttons.
Jim '98 XJ
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