If you are absolutely sure the leak is coming out of the bottom of the disposal it's going to be a replacement thing. However, I suggest you make sure it's not leaking near the top connection to the sink and maybe running down the back side giving the appearance of leaking from the bottom. The top location does have a gasket and can be replaced.
Dennis (cut2it)
C&onstructi&on C&onsultant
Over 40 yrs. as General Contractor for new const. & remodel - retired with time for you.