Due to space constraints, I had to sell my Polysix. I'm leaving these pages here for reference, but it is unlikely that there will be any updates in this section

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The original tactile switches for bank and program selection, as well as the key assign and arpeggiator eventually fail.  Luckily these are still in production; the originals are made by Alps (Model number SKHCAB) and are the same buttons used in the Roland TR-808 and TR-909 among others.  The original Alps switch specifications are available for viewing  (PDF).  To summarize, they are 12mm square, 4.3mm tall and have an operating force of 130gf. 

I've also located a few manufacturers that claim to have exact replacement parts available.  Please note that I have not confirmed that these parts fit, but the manufacturers claim they are exact replacements for the Alps parts.  Here are the cross references that I have found:

Manufacturer	Part Number	Supplier (supplier part number)
Alps (OEM)	SKHCAB
Omron	B3F-4000	Mouser (653-B3F-4000)
E-Switch	TL1100DF160Q	Mouser (612-TL1100D)

I hope to order new tact switches on my next Mouser order.   Perhaps I'll buy some both the Omron and E-Switch products and compare them.   It's only a few dollars to replace all of the switches in the keyboard, so I'll probably experiment with both brands.