When I just brought the mill home, the pneumatic motor driven
vari-speed adjustment worked well. Now it has become extremely
sluggish and seems to hiss and leak a lot of air when working,
especially badly when decreasing speed.

This is driven by this pneumatic valve:

http://picasaweb.google.com/lh/photo...eat=directlink

This seems to be a similar trouble to what I had with the brake
valve. Probably some rotted seal. Unlike that brake valve, this speed
valve has no markings. The procedure to fix it would seem to be to
take it apart and see what went wrong. Before I do so, I wanted to ask
for any suggestions etc about this, I would hate to fsck it up,
esp. since I am not sure what make/model it is.

If anyone knows who made it, , I woud be really grateful.