This experience is from an old Lester Player that I still have.  The
work was done about 10-12 years ago.  About 3 of the bass strings
wouldn't hold at all, with problems in some of the tenor strings.
When you got the string in tune and released tension on the tuning
lever, the string would go back down to its original pitch.  Hammering
in the tuning pins didn't help completely.  This holding problem was
not localized to any specific area on the pin block so I didn't think
it was a crack in the pin block wood.

Most of the tuning pins seemed loose and I didn't want to restring the
piano, so I used "Pin-Tite".  I placed the upright piano on its back
and applied the "Pin-Tite" in groups of about 30-50 pins at a time.
The first two applications were done within 15-20 minutes from each
other.  I then waited for one day and repeated the application a third
and fourth time.  The piano was then tuned.

The tuning went well.  All of the pins held, even though the extremely
loose pins were not as tight.  The piano has kept its tune quite well
over the past ten years even though it has only been tuned about four
times since.  I noticed that when I tuned it, the problem pins would
loosen up a little more as time went on.  On the last tuning, one of the
bass strings started to slip again.  I fixed this by using an oversized
pin.

Note: I don't like mixing tuning pin sizes like I did here.  This
causes problems later when the entire piano is re-strung.

The piano has been in my mountain cabin for about six years, where it
sees temperatures of -10 to 75 degrees F between winter and summer.  It
hasn't been tuned for about 3-4 years and still doesn't sound too bad.

I don't think that "Pin-Tite" is the ultimate solution but it does help
delay a repining job.  If you use it, don't let it dry on your metal
plate.  I have seen many piano plates badly discolored and areas where
dirt accumulates because of large amounts of the tightening solution
being poured onto the plate and pooling.

Take the time to apply it properly.  Place a few drops on each side of
the pin and let the surface tension take it down.  Remember that there
is about 1/4 inch between the top of the plate and the wood pin block
below.  If you have wood tuning pin bushings between the pin and the
plate, you may not be getting the solution down to the pin block at
all.  The holding power of the bushing is much less but it will still
help in holding the pin in position.

Pete Knobloch (Tempe AZ)