The buttons on this synth don't reliably work, and the pots are very gummy.

Buttons

Sometimes a button press will not be sensed, other times it will trigger multiple times.  Thankfully another owner had this issue and discussed taking them apart.  As stated by them, these are Marquardt series 6450 buttons.  They are well made, with wiping contacts and can be disassembled to be repaired.  You can still purchase them, but I figured it would be easier and much cheaper to try first to just clean them.

I think their failing point isn't the wiping contact, but rather the pivot point between the flex contact and the fixed one.  They seem to corrode at that contact, suggesting incompatible metal types between them.  But not too difficult to repair.

With the front panel board removed, the button tops can be removed by using something thin to press inwards on both sides.  As this has small plastic clips, I wouldn't pry or lever, but instead just press inwards.  I used a pair of tweezers and a thin flat blade screwdriver.

As soon as you get the first one out you can more easily see how it works and quickly get the rest.  The picture below will help see how they are shaped.

The flex contact can be easily removed with a pair of tweezers.  I pulled them all out and cleaned by putting them in a small jar with some contact cleaning spray, and swished them around.  This type of spray tends to get everywhere, so I keep some on this jar for finer application, or in this case just dropping all the contacts in.

After a min or so of swishing, I just picked them out with tweezers and set to dry.

The contacts in the base also needed to be cleaned.

I used a small glue applicator bottle to put a couple drops of the contact cleaner on them, and brushed a little with these cleaning swabs.  Unlike "qtips", there is very little cotton on the tip so it fits in smaller areas and doesn't leave cotton threads that pull off.

These are available on aliexpress for like 2$ for 300 delivered.

After drying thoroughly, the flex contact can be reinstalled carefully with tweezers.  Put one end in, and slightly  bend it to get the other end as well.  I found it easiest with curved tweezers holding the zig zag part, lining in the curled end, then bending to get the sharp in on the contact.

Here's a quick video

Button cleaning

While the button tops were off, I gave them and the knobs a good cleaning with soapy water and a nylon brush.

Then let them dry.

Pots

The friction grease in the pots had gone gummy, such that turning them was quite a bit of friction.  While they still worked fine, the effort was tiring when trying to turn them a lot when being creative with the synth.

This video is the best one I found which discusses the issue and how to fix it.  It's long, so you can skip by much of it, but I believe it is correct. (He correctly points to the issues with using contact cleaner on pots as well)

The problem is that to do this one needs to disassemble the pots, and to do that with these, they would all have to be desoldered from the PCB.

I decided it would be best to see what I can do without disassembling it and giving it a try.  If it isn't goo enough I can remove the board again and then go further.  Thankfully the front panel board is the easiest to remove.

I used isopropyl alcohol, trying to wick it down between the shaft and the collar, rotating the knob back and forth to work it in.  This made a huge positive difference.  It remains to be seen if this will stay, or if they will gum up again.

I'll readdress if I need to later.

I did also look for replacements.  I was unable to find the original manufacturer, or direct alternates on pot vendors product lists, or in component distributors.  I can get the Nord resold ones through their regional representative, for 9$ each.  For 19 pots, and given these should only be 2, maybe 3$, this seemed excessive.

Finally it all goes back together and working.  I'll use it for a bit and see how it goes and if anything else comes up.