Hi Wolf,  Most of the lead dust from the elbows will be in the pump,
if it still can draw a vacuum sufficient to move the debris.  While not
desirable, this debris will not result in the failure your describe.

Self-help to fix the problem is fine, but an owner who does no
restoration usually draws the wrong conclusion about what needs to be
done.  In general, if the tubing is bad, so are many other parts, too.
The instrument is probably in need of complete restoration, but who
knows?

If the stack bolts are tight -- the ones that hold the stack together
and to the piano -- a vacuum applied to the main stack nipples should
produce strong playing.  Use a household vacuum, this bypasses
everything else.  If the results are poor, the stack pneumatics and
valves are highly suspect.  Do one side at a time and use no roll.
Run your finger up and down the tracker bar holes to test the notes.
If the stack seems okay then assume the pump and all circuits connected
to it are leaking.

There is no one correct answer to your question.  It is a guessing game
for those responding, as there is insufficient information to make a
definitive conclusion.  The above suggestion is a start at a systematic
"shake-down".  Using knowledge of the system, a process of elimination
to find leaks should be employed.   Don't inhale the lead dust.

Good luck!

Bob Taylor