Hello All,  I've had a number of these Aeolian Theme valve units apart
over the years and I don't ever remember any problems getting them back
in, but there's always a first time.

In most cases the ones I dealt with seemed to have a green coloured
grease around the brass treads, no doubt some kind of lubricant applied
by the manufacturer during assembly, possibly beef tallow.  It would
most likely have been used to seal the wood to the threads to prevent
leakage and to allow adjustment of the valve.  Over the years it would
have turned green due to the acids in the wood reacting with the brass.

I would try applying a little pure beeswax diluted with white spirit,
or apply any proprietary brand of wax polish.  You could also try
a silicone-based grease but I have no experience with this.

The thread is quite coarse, most likely not a BS Whitworth but possibly
UNC.  A local tool supplier will be able to match the thread and supply
you with a suitable tap if you need to go down that route.

Just my ten bob's worth,
Paul Camps

 [ Discussions and tables of screw threads are at
 [ http://en.wikipedia.org/wiki/British_Standard_Whitworth 
 [ http://en.wikipedia.org/wiki/Unified_Thread_Standard 
 [ http://www.metal-mart.com/Guides/Tap_Drill_Sizes.htm 
 [ -- Robbie