It may or may not need an adjustment in the coming years, but if it does, then what?
Is it out of spec now? If it isn't then there's no reason to think it ever will be.
I suppose it could go on living for qualitative see-if-something's-there use
That's actually its main purpose.
Oscilloscopes aren't multimeters. You shouldn't expect highly accurate voltage measurements from them.
Most DSOs use 8-bit ADCs attached to circuitry that's designed to respond to high frequencies. This means you have about 1% accuracy under
ideal conditions (and that's
only when your vertical gain is set so that the signal occupies the whole screen).
The specs for the DS1054Z are:
DC Gain Accuracy: <10 mV: ±4% full scale, ?10 mV: ±3% full scale
DC Offset Accuracy: ±0.1 div ±2 mV ±1% offset value
1% offset error + 3% gain error could add up to 4%. Add in the ADC error, improper vertical scale setting, some RF noise from the lights, imperfect probing, etc. and you can easily have 5-10% error in the on-screen numbers.
Bottom line: Oscilloscopes
aren't multimeters.
(Yes, I'm sure there's some old green-screen "Tek" that's sub-1% accurate, but... )
Yes, I've tried to find a service manual. Perhaps others have better Google-Fu than I. However, I vaguely recall a post or two about the lack of much technical information about these scopes. Hence, my ponderings.
I doubt they have anything more than their self-calibration function.