There is a bit of draining after a minute or so after flushing the toilet.
Tried replacing the flapper. Pretty much got the same result. I'm using
the popular orange 'Corky' flapper sold at Home Depot. There is a slight
imperfection in the brass pipe (?) that the flapper rests on. Don't know if
that is that is the problem. I'm wondering if there is a way to get a
better seal from this flapper.

The toilet is an older 'Standard' toilet probably 30 years old or so. The
plumber across the street recommends I replace the whole toilet unit with
all it's fixtures. I figure that might run me $200+ or so with
installation. I'd rather settle for the temporary $5.00 fix if possible.