I need to replace a cracked, plastic laundry tub. It's self-rimming and is mounted on a formica-covered counter. The original installation was in 1999, and they used a lot of caulk, which appears to be either elastomeric latex or silicone rubber. It won't budge. Cut with a utility knife around the outside but it would penetrate only a tenth inch before the blade was pinched tight. Put a jack under the sink, but the counter top started rising, even with my helper leaning on it. Clamped the front of the counter to top edge of access door and tried the jack. Back of counter started to rise. Cut sink loose with saber saw where rim transitions to vertical walls of sink, which was easy, but rim is is still stuck to counter. Tried the utility knife and prying from the inside of rim, which didn't work. And tried softening caulk with heat gun, which didn't work. I might remove the rim with several hours of tedious milling with a Dremel tool, which would raise clouds of nasty plastic dust, but then again the tool bit would probably clog a lot with the old caulk. Thought of using a router, but sink is surrounded by a back-splash with only a few inches between back-splash and the rim, so not enough room for a router.
Unless someone can think of something better, it's time for a new counter top. BTW, the replacement sink is stainless steel, has same dimensions as old sink, uses clamps to hold it down and won't need much caulk.