I once opened for the Spinners (UK folk group) at a concert in the early 70s. I saw that their harmonicas were each sitting in a pint glass of warm water . . .

Of course I asked why . . . they explained and I tried it. To say it harms the harmonicas isn't altogether true as I too have some Hohner Blues harps 'left over' from that period.

Just try it, use your most 'muffled' harmonica, swish it about a bit then let it soak for 5 minutes or so then gently shake out the water. The sound improvement is stunning.

I've been doing it for the last 40 odd years and haven't had one fall apart yet - I'd pay the price anyway as it really does the job.

Let me know how you get on.