I assume the gunge is baked on toner, if so you can sometimes remove it with
warm soapy water but the rollers are very easy to damage, almost no pressure
should be applied to the roller just a very gentle wipe or the roller may start
to crease. There is also a product available called Toner Remover, it is very
good and has to be used in the same way as described above. I did a quick arch
for "laser toner remover" and found several sites. Acetone works but I would
not use this on a roller, since I am concerned that it may destroy the surface.