This same phenomenon cost me a set of decent Marples wood chisels. Purchased in the early sixties they were fine for twenty odd years, then I noticed an oily feel to the red and yellow, two tone handles. This became more and more pronounced, with the "oil" soaking into the wooden rack. As the leakage continued, the handles became smaller and smaller until the tool were no longer useable; not a great loss, as by then the blades had been sharpened down to short stubs. Since then, I have lost a couple of screw drivers in the same way and, only last week, found and old and abused "dig it, poke it and prise it" screwdriver at the bottom of a drawer, laying in a pool of its own 'body fluids'.
I have just assumed that the plastic material has a limited life and remains stable for a while, before starting to decompose. My response: shrug, fit wooden handles or replace the tool.