Reg Smith says he was buying limited supplies of slotted screws from
the UK.  The only supplier that I am aware of in the UK is Nettlefolds;
they were for many, many years the mainstay of the wood screw industry
and in the final years of Ashorne Hall I dealt with them direct.

Nettlefolds used to supply all countersunk and round head wood screws
in popular sizes.  Roundheads tended to be in Japan-black, but this
could be buffed off.  Anything from 4" x No. 12 gauge down to 1/4" x
No. 1 gauge was readily available from stock.  Any longer sizes would
require a special production run and great expense.

Countersunk screws were available in plain steel or 'self colour', as
it tends to say on the box, and of course plated which I think Reg did
not want.  I still have a very large stock of these screws, but sadly
they are not for sale as I'm still using them myself.

Before metrification a No. 12 gauge screw required a 1/4-inch diameter
drill to provide a clearance hole and a 3/16" drill for piloting.  Now
you find a 12 gauge has a 3/16" shank which requires a smaller pilot
drill.  But this is the kind of progress that causes us restorers
problems.

I seem to remember that Nettlefolds were based in Sheffield, but I have
not used them for five or six years.  I'm sure that others here in the
UK will have more up-to-date info.

With regard to the sustaining pneumatic that releases slowly, I would
agree with the posting from Eliyahu Shahar -- it's most likely the
valve travel at fault.  I have worked on the Red Welte system and
I know that valve travel can be critical.  If the sustaining motor
is quick to collapse but slow to release, and given that there is no
linkage or other mechanical defect, then in my opinion it only leaves
the valve clearance/travel.

Just my two-pence worth,
Paul Camps, UK