Buy quality and only cry once. I have a Lubelocker on my Grand Marquis... I will never go back to RTV... LL seals perfectly, no drips, no mess, and best of all no double torqueing, or interminable waiting for the RTV to cure and only then discovering you have a leak... with the LL you open the diff, clean it out, close it up, refill, and you are back on the road.
If you off-road and the diff goes under water (for the record I do not off-road with my Grand Marquis, and if its diff ever went under water, something must have gone terribly wrong), a Lubelocker will save you beaucoup time and aggravation... I wish I had switched sooner...