So far no sound at all on the right side. It could be that they just need to charge up. It could also be that some connections are corroded.
As for the 'broken' pair, although these things have a headphone plug on them, they need a fairly beefy source. This is why they usually come with a box that lets you plug them into a speaker amp.
Plugged into a source that makes most headphones loud, they may only whisper. The headphone amp i plugged mine into is configured to make very inefficient headphones quite loud - it's beefier and meaner than most. So it could be that they're working just fine.
If you buy a pair, unless you enjoy taking things apart and making them better than they were when you started, you'd be better off starting your electrostatic experience somewhere else. These kosses are as old as 1969 and even if they are truly new old stock, they need some attention to be their best - not all of the materials they used hold up to the test of 30+ years on the shelf.
people may even sell refurbished sets, but it's hard to say how much they're worth. I paid less than $15 for my set.