Andy Taylor asked about cracked plates.  I've repaired several plates
and the last thing I would do is braze or weld it.  Many will tell you,
"I know a welder who can weld cast iron," and I admit there are some
that have held up.  I'm just guessing, but I believe there may be more
that have failed.  I've seen a couple.

Cast iron shrinks dramatically; I think it is 6%.  To weld cast iron
would require the whole plate to be heated to 1200 degrees, then welded
and allowed to cool over 6 hours.  If you tried to weld a spoke in a
wheel the expansion alone would cause it to crack immediately.  Also,
the rapid cooling would harden the material and cause it to be brittle,
increasing its tendency to crack where the weld ends.

I had a grand piano that had two cracks in the struts.  By studying the
plate it was obvious that there was a definite weak spot that was in
the design.  When I loosened the plate mounting bolts, the crack closed
up part way.  Now I knew what caused it to crack.  The plate had been
torqued in the worst direction before it was strung and then the
tension caused the weak spot to let go.

I repaired this by cutting the plate strut so that I could put a splint
of 7/16" steel bar stock across the crack and extending it beyond the
weak spot, using screws, dowel pins and steel-filled epoxy.  It was
shaped and sprayed so that the patch was invisible.  I corrected the
mounting stress by mixing epoxy with sawdust and bolting the plate flat
and allowing the epoxy to cure that had been squeezed out at the low
spot before installing the bolts.  This was where the plate was screwed
down to the pinblock.

I try to repair plates by reinforcing and patching with steel, screws
and epoxy where I can do it and not interfere with anything and try to
do it as cosmetic as possible.

There is a company in Turlock CA that makes "Castmaster" stitching
pins with spiralhook threads that will pull the two sides of a crack
together and lock them in place.  These pins when overlapped will give
an airtight seal.  They were developed for repairing cast iron blocks
and heads for engines.  The company is Lock-N-Stitch Inc.  Looks like a
good approach for certain types of plate cracks, but I haven't tried it
yet.  "Look Ma -- No heat!"

Andy, from your description, I think your crack may have been there
since day one, and it probably happened when the plate first cooled.
I don't think you have anything to worry about.  And don't forget that
my free advice has a money back guarantee.

regards

Carl Meyer