NEC blue ovals - advice on cleaning

[thegoldenmandenis]

I've got an NEC blue oval keyboard but the switches really need a clean. I have ever been trying to find out if it's possible to remove them from the board or open them up, and it seems as though it isn't, not without desoldering and potentially breaking the switch body. Opening the switch up to get to the innards seems to be completely impossible without irreparably breaking the plastic rivets holding the switch together. Can anyone confirm that understanding is correct?

If that is right, what's the best way to clean them? Is it just not possible?