Just to back up Tim Trager's comments:  I recently visited the owner
of a 41-key Bruder organ which has been neglected for decades.  The
owner -- as quite a few others, I must say -- did not hear that the
organ, although mechanically sound, performed very badly (many pipes
not speaking, ciphers, exchanged pipes etc.).  After just hearing
a test strip, I told him what (at least) was wrong; a (church) organ
builder from a neighboring village then regulated the valves and put
the pipes in the correct order.

When I visited him some time later, only one valve was still misbehaving;
after opening the valve chest (the first time in my life I did this for
a large organ!) we found the culprit by visual inspection, moved the
valve to a correct position, closed everything, and voila -- it works.

Obviously, this does not mean that one *should* neglect an organ ;-)
but it shows that they were built to last, and built to work with only
minor troubleshooting and maintenance.

Regards
Harald M. Mueller
Grafing b. Muenchen
Germany