The problem you describe, of notes playing weakly when played rapidly,
is usually a sign of too much valve travel.  The only time a valve
is leaking (assuming the system is airtight) is when it is in motion.
The valve should travel _only_ 0.035" with 0.033" the minimum allowable
and 0.040" the maximum.

This indicates the need for a valve rebuild and if it was rebuilt then
a micrometer wasn't used on the valve travel.  You should check this
now and plan to rebuild or at least re-regulate at this time.

Doug L. Bullock
http://thepianoworld.com/