Never hasn't worked but we don't subscribe to the spotless gasket surfaces either. Scrape off anything easy, leave the cured stuff in the low spots, peel off the boogers, seal it.
that's the part I think I may try with the lubelocker. My previous uses have been with a spotless surface. If it leaks again I'll just go back to RTV but stop waiting for the cure time. Or at the very least, just let it sit overnight instead of waiting the full 24 hours.