Melodica Malfunction Revisited

Some time ago I wrote about the sticky key issue I experienced with my super-cheap Hohner Student 32 Melodica and the steps I took to correct the problem.

Since then I have played a few parts on a few different tracks and have found that the problem has returned, but in a less drastic way. While the keys do not now stick when depressed, they stick when not played. Depressing the keys unsticks. The part of the key in the interior that closes the gasket now sticks to the gasket. With a little playing the problem lessens but it is still irritating and impedes fluid playing. I'm no melodica virtuouso but I suspect that any player whatever his level of proficiency would find this unacceptable.

At the moment I have no idea how this can be corrected. Clearly the yellow rubber foam can't be replaced as it is moulded very specifically to the shape required to make an airtight seal.
Nothing that comes to mind (a silicon lubricant? talcum powder?) strikes me as a viable solution.

Any tips or recommendations are welcome.

Apart from that, the keys are really too small on this instrument and when funds are not so tight I hope to buy a bigger, better melodica made from superior materials. Recommendations invited!