Ever since I installed a Universal-Rundle tall commode 10 years ago,
I've had a recurring problem with a very small leak around the right
mounting bolt which securs the tank to the bowl. I've had to
retighten the bolt at least every year. The left one has never
leaked.

Last week I removed the toilet so I could put down new vinyl tile
flooring. While it was out, I bought a new tank mounting kit at
Lowes....big donut center gasket, two new long bolts, two nuts and
four each rubber or fabric washer and flat metal washers. I thought
for sure the new mounting hardware would fix the problem. However,
after reinstalling the commode there's STILL a small leak around just
the right bolt. Tried backing off the other bolt and retightening the
right one...no luck.

I drained, dried and carefully inspected the insides of the tank. I
noticed there are 1/32 to 1/16" raised letters in the porcelain which
say MADE IN USA in the bottom. Unfortunatele, part of the 'M' and the
'A' letters are so close to the right hole that the rubber washer has
to fit over them. I'm thinking they create just enough of an
obstruction that the the washer will not seal in that area. What I'd
like to know from you plumbing-savy types is the following:

1. Can I file or sand the raised letters off the porcelain without
harming its waterproofing ability?

2. If sanding porcelain could be problematic, I'm considering putting
a small amount of either plumber's putty, pipe joint compound (aka
pipe dope) or silicone caulk/adhesive between the rubber washer and
the letters to try to seal the small leak. Which of those products
would hold up best under water without harming the washer?