Josh writes:

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:

I had a leak and did the following to solve it by adding an extra
Rubber washer/metal washer/nut sandwich around the tank part.

From the inside of the tank assemble the following:
Bolt head
Metal washer
Rubber/fiber washer
Tank porcelain
Rubber/fiber washer
Metal washer
Nut --- tighten this nut independently to get a good seal around
the tank hole independent of the connection to the
bowl. This allows you to tighten down without
leveraging and cracking the porcelain bowl
Bowl porcelain
Rubber/fiber washer
Metal washer
Nut --- tighten this to secure tank to bowl and prevent
leaking from the drain tank drain seal.

Also to confirm whether leak is coming from bolt hole in tank or from
seal with bowl do the following:
- If it leaks all the time, it is leaking from the tank (either the
bolt hole, a crack in the porcelain, or aound the drain gasket)
- If it leaks only when you flush, then the tank may not be seating
tightly against the bowl.

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?

Adding some pipe dope around the bolt and washers in the first
sandwich can help if still leaking.

Entombing with silicon is to me a last resort and a sign of a
kludgey-DIY repair.