[michaelbsc]

Is it feasible to soak the film in white vinegar to attempt to remove the deposit?

Vinegar is dirt cheap where I live, and I imagine it isn't expensive anywhere.

So a couple of bucks for a bottle of vinegar is you don't happen to have it already in the kitchen, and cut it to 1+3 is where I would start. Not sure what concentration would be recommended to clean calcium stains. But 1+3 should be about 1-2% acetic acid for most grocery store brands.