Wow, I can't tell you just how satisfying it is to have finally retrieved the last corroded battery from my keyboard. I tried baking powder, GT85 lubricant, then white wine vinegar and I think it was the latter, combined with slamming the keyboard against my desk that did the job.
Next question: how do you get a cleaning rag out of a wireless keyboard battery slot??
Just kidding! Well now the batteries are out I hope it will work, but after pouring all that stuff down the tube I'll wait a couple of days before trying it.