TubeNet

A quick search for 'oiling of rotary valves' turned up several hits. I sort of like this one:
http://www.lyricbrass.com/spang/oilroto ... %20valves'

The fact that your 4th rotor all of a sudden got 'scratchy' concerns me. There might be a chance that you have some type of hard deposit lodged between the rotor and the casing... or perhaps even some damage. Maybe it's time for the horn to be chemically cleaned and serviced by a professional.

There's a really good online streaming video tutorial here:

http://www.uni.edu/drfun/FunderburkIndex.html

by Jeff Funderburk that covers basic maintenance of rotary instruments. I believe you can download the whole thing for "perusal at your leisure" (nod, nod, wink, wink). It includes some great info on where to oil & what to use.

Hope that helps

Russ