There are many solutions....
You can buy replacements (I sell them at
http://www.minimoogs.com.)
You can put in trims for the range that are 800 ohm instead of 1K and obtain less range for the same travel.
You can drill holes or add sub-boards to accommodate 25 turn cermet multi-turns.
But be forewarned that you must mount them to align with rear cover trim holes.
You can change or add resistors to allow less range for both trims types.
You can even go so far as putting in selected resistors and pots with
much less range, thus allowing for only a few semitones of tuning span.
Generally I'll first wash a vco board and flush out the trims, drying them off using compressed air.
If they're still iffy after that, I'll usually replace them.
I do have artwork for PCB sub-boards that hold multiturns, but out of finished boards at the moment.
That solution is the most difficult, but arguably the most stable both in terms of vibration and temperature sensitivity.
It's also not stock, which some people take objection to and I can understand such concerns.
I also hugely recommend replacing all of the VCO summer resistors with new precision matched triplet sets.
These are all the resistors along the right side of the board (and one at the bottom.)
They are what's responsible for feeding in all CVs to the VCOs and must be matched perfectly as sets.
Over time they can drift in value and make it much more difficult to calibrate everything perfectly.
I sell those too, but you're welcome to make your own sets or check what the values are of the ones already installed.
You
must have an accurate DMM for this if you do it yourself.
4.5 digits minimum.
Finally, remember it's a voltage controlled synth and all voltages and tunings are dependent on the power supply being stable.
Since the power supply uses the same type of wirewound trims as the VCOs and are likely the same age, those trims should be also be addressed.
If they wander, so does the whole instrument.
Again, it's possible to range-limit those trims so they span very little change from full CW to full CCW.
They're considerably easier to swap with good multiturns than the VCOs too.
Cermet multiturns tend to have less temperature drift than wirewounds too and being so close to the heatsinks, it's important they don't drift from temperature.
And suffice to say, tuning an instrument with trims that provide 10-25 turns is a whole lot easier than adjusting trims that provide less than one single turn of travel.
Hope something above helps.
Good luck!