You cant use it. Its the copper and other stuff in there that'll whack out the readings.
One of thoses little containers of transducer paint lasts for years.
What I do is borrow it from a friend every season after he comes over for his annual sandpaper allowence. Most people wont mind letting you borrow a coat or 2 because it'll dry out before the container could ever be used up.
It's cheap to buy also.
alan