JohnL:

I've seen those Fernco couplings used to replace chrome plated p-traps, and that's probably your best bet if you don't want to remove your cabinet.

But, all of those old chrome plated p-traps were a problem waiting to happen from the day they were made. That's because the metal that was chrome plated was brass, which is an alloy of copper and zinc, and zinc is a highly reactive metal.

If you've ever gone to change the rubber washer in an old water valve, you'll often find that the bibb screw is reddish brown in colour and crumbles under the force of your screw driver. That's because the head of the brass screw has been dezincified. The valve body itself is still strong because it's not made of brass, it's made of bronze, an alloy of copper and tin. Tin isn't nearly as reactive as zinc.

In a chrome plated brass p-trap, it'll be the brass below the water line in the trap that dezincifies the fastest and the soonest. Hopefully there's still some strength left in that trap arm since it was above the water line for most of it's life. But I'd be gentle tightening up the clamp that squeezes the Fernco onto the chrome plated brass. You don't want to crush that tubing.

And, if that doesn't work, then it's back to Plan A with removing the cabinet, opening up the wall and getting all of that chrome plated crap outta there.