IRS leak on one side on 1990 Ford Thunderbird SC

Leaks on one side only between wheel and center
there is also a small thump when starting out.

Asked by for the 1990 Ford Thunderbird SC
Obviously the leak needs to be stopped first and foremost. Sounds like an axle seal. The thump could be anything from a mount that's worn to a universal joint issue to a ring and pinion issue. A good inspection will figure it out.